diff --git a/src/d_netcmd.c b/src/d_netcmd.c
index 725e50a6c..9dc9040a3 100644
--- a/src/d_netcmd.c
+++ b/src/d_netcmd.c
@@ -184,6 +184,7 @@ static void Command_AcceptInvite_f(void);
 static void Command_RejectInvite_f(void);
 static void Command_LeaveParty_f(void);
 
+static void Command_Addfilelocal(void);
 static void Command_Addfile(void);
 static void Command_ListWADS_f(void);
 static void Command_ListDoomednums_f(void);
@@ -858,6 +859,7 @@ void D_RegisterServerCommands(void)
 	COM_AddCommand("showmap", Command_Showmap_f);
 	COM_AddCommand("maphash", Command_Maphash_f);
 
+	COM_AddCommand("addfilelocal", Command_Addfilelocal);
 	COM_AddCommand("addfile", Command_Addfile);
 	COM_AddCommand("listwad", Command_ListWADS_f);
 	COM_AddCommand("listmapthings", Command_ListDoomednums_f);
@@ -4763,6 +4765,44 @@ static void Got_RunSOCcmd(UINT8 **cp, INT32 playernum)
 	G_SetGameModified(true, false);
 }
 
+static void Command_Addfilelocal(void)
+{
+	const char *fn;
+	INT32 i;
+	size_t docompat = COM_CheckPartialParm("-c");
+	size_t nocompat = COM_CheckPartialParm("-n");
+	wadcompat_t compat = WC_AUTO;
+
+	if (docompat && nocompat)
+	{
+		CONS_Printf(M_GetText("Please specify only one of -c or -n\n"));
+		return;
+	}
+	else if (docompat)
+		compat = WC_ON;
+	else if (nocompat)
+		compat = WC_OFF;
+
+	if (COM_Argc() != 2 + (docompat || nocompat))
+	{
+		CONS_Printf(M_GetText("addfilelocal [-c|-n] <filename.pk3/wad/lua/soc>: Load local add-on\n"
+									"-c forces compatmode, -n disables it.\n"));
+		return;
+	}
+	else
+		fn = COM_Argv(1);
+
+	// Disallow non-printing characters and semicolons.
+	for (i = 0; fn[i] != '\0'; i++)
+		if (!isprint(fn[i]) || fn[i] == ';')
+			return;
+
+	// Add any wad file, ignoring checks for if it contains complex things like
+	// lua. Great for complex but client-side customizations, like different
+	// level cards or anything like that.
+	P_AddWadFile(fn, compat, true);
+}
+
 /** Adds a pwad at runtime.
   * Searches for sounds, maps, music, new images.
   */
@@ -4856,7 +4896,7 @@ static void Command_Addfile(void)
 		// Add file on your client directly if it is trivial, or you aren't in a netgame.
 		if (!(netgame || multiplayer) || musiconly)
 		{
-			P_AddWadFile(fn, compat);
+			P_AddWadFile(fn, compat, false);
 			addedfiles[numfilesadded++] = fn;
 			continue;
 		}
@@ -4996,7 +5036,7 @@ static void Got_Addfilecmd(UINT8 **cp, INT32 playernum)
 
 	ncs = findfile(filename, filehash, true);
 
-	if (ncs != FS_FOUND || !P_AddWadFile(filename, compat))
+	if (ncs != FS_FOUND || !P_AddWadFile(filename, compat, false))
 	{
 		Command_ExitGame_f();
 		if (ncs == FS_FOUND)
diff --git a/src/d_netfil.c b/src/d_netfil.c
index 469b8df3f..b107637af 100644
--- a/src/d_netfil.c
+++ b/src/d_netfil.c
@@ -563,7 +563,7 @@ INT32 CL_CheckFiles(void)
 			// CONS_Printf("checking %d of %d / %d of %d?\n", i, fileneedednum, j, numwadfiles);
 			// CONS_Printf("i: %s / j: %s \n", fileneeded[i].filename, wadfiles[j]->filename);
 			
-			if (j < numwadfiles && !wadfiles[j]->important)
+			if (j < numwadfiles && !wadfiles[j]->important && !wadfiles[j]->localfile)
 			{
 				// Unimportant on our side.
 				++j;
@@ -656,7 +656,7 @@ boolean CL_LoadServerFiles(void)
 			continue; // Already loaded
 		else if (fileneeded[i].status == FS_FOUND)
 		{
-			P_PartialAddWadFile(fileneeded[i].filename, fileneeded[i].compatmode ? WC_ON : WC_OFF);
+			P_PartialAddWadFile(fileneeded[i].filename, fileneeded[i].compatmode ? WC_ON : WC_OFF, false);
 			G_SetGameModified(true, false);
 			fileneeded[i].status = FS_OPEN;
 			return false;
diff --git a/src/g_demo.c b/src/g_demo.c
index 4ece52183..94e77c897 100644
--- a/src/g_demo.c
+++ b/src/g_demo.c
@@ -3082,7 +3082,7 @@ static void G_LoadDemoExtraFiles(demoheader_t *header)
 			}
 			else
 			{
-				P_PartialAddWadFile(file->filename, file->compatmode ? WC_ON : WC_OFF);
+				P_PartialAddWadFile(file->filename, file->compatmode ? WC_ON : WC_OFF, false);
 			}
 		}
 	}
diff --git a/src/p_setup.c b/src/p_setup.c
index fd29591b7..d7aec5693 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -9128,7 +9128,7 @@ boolean P_RunSOC(const char *socfilename)
 	lumpnum_t lump;
 
 	if (strstr(socfilename, ".soc") != NULL)
-		return P_AddWadFile(socfilename, WC_AUTO);
+		return P_AddWadFile(socfilename, WC_AUTO, false);
 
 	lump = W_CheckNumForName(socfilename);
 	if (lump == LUMPERROR)
@@ -9348,11 +9348,11 @@ UINT8 P_InitMapData(boolean existingmapheaders)
 // Add a wadfile to the active wad files,
 // replace sounds, musics, patches, textures, sprites and maps
 //
-boolean P_AddWadFile(const char *wadfilename, wadcompat_t compat)
+boolean P_AddWadFile(const char *wadfilename, wadcompat_t compat, boolean local)
 {
 	UINT16 wadnum;
 
-	if ((wadnum = P_PartialAddWadFile(wadfilename, compat)) == UINT16_MAX)
+	if ((wadnum = P_PartialAddWadFile(wadfilename, compat, local)) == UINT16_MAX)
 		return false;
 
 	P_MultiSetupWadFiles(true);
@@ -9450,7 +9450,7 @@ static boolean P_CheckVoteReplacements(char *name)
 // Add a WAD file and do the per-WAD setup stages.
 // Call P_MultiSetupWadFiles as soon as possible after any number of these.
 //
-UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat)
+UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat, boolean local)
 {
 	size_t i;
 	UINT16 numlumps, wadnum;
@@ -9486,6 +9486,9 @@ UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat)
 	{
 		partadd_important = true;
 	}
+
+	wadfiles[wadnum]->localfile = local;
+
 	if (partadd_stage != 0)
 	{
 		partadd_earliestfile = wadnum;
@@ -9573,14 +9576,20 @@ UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat)
 	K_InitBrightmapsPwad(wadnum);
 
 	// Reload TERRAIN
-	if (K_InitTerrainPwad(wadnum))
-		partadd_terrainloaded = true;
+	if (!local)
+	{
+		if (K_InitTerrainPwad(wadnum))
+			partadd_terrainloaded = true;
+	}
 
 	//
 	// look for skins
 	//
-	R_AddSkins(wadnum); // faB: wadfile index in wadfiles[]
-	R_PatchSkins(wadnum); // toast: PATCH PATCH
+	if (!local)
+	{
+		R_AddSkins(wadnum); // faB: wadfile index in wadfiles[]
+		R_PatchSkins(wadnum); // toast: PATCH PATCH
+	}
 
 	//
 	// edit music defs
diff --git a/src/p_setup.h b/src/p_setup.h
index 8c6d03bf1..53e0d274a 100644
--- a/src/p_setup.h
+++ b/src/p_setup.h
@@ -88,7 +88,7 @@ void P_PostLoadLevel(void);
 void HWR_LoadLevel(void);
 #endif
 void P_UnloadLevel(void);
-boolean P_AddWadFile(const char *wadfilename, wadcompat_t compat);
+boolean P_AddWadFile(const char *wadfilename, wadcompat_t compat, boolean local);
 
 #define MAPRET_ADDED (1)
 #define MAPRET_CURRENTREPLACED (1<<1)
@@ -100,7 +100,7 @@ extern INT16 wadnamemap;
 // WARNING: The following functions should be grouped as follows:
 // any amount of PartialAdds followed by MultiSetups until returned true,
 // as soon as possible.
-UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat);
+UINT16 P_PartialAddWadFile(const char *wadfilename, wadcompat_t compat, boolean local);
 // Run a single stage of multisetup, or all of them if fullsetup set.
 //   fullsetup true: run everything
 //   otherwise
diff --git a/src/sdl/i_video.cpp b/src/sdl/i_video.cpp
index 28bf4c54e..b6dc062a6 100644
--- a/src/sdl/i_video.cpp
+++ b/src/sdl/i_video.cpp
@@ -1142,7 +1142,7 @@ void I_GetEvent(void)
 				break;
 			case SDL_DROPFILE:
 				dropped_filedir = evt.drop.file;
-				P_AddWadFile(dropped_filedir, WC_AUTO);
+				P_AddWadFile(dropped_filedir, WC_AUTO, false);
 				SDL_free(dropped_filedir);    // Free dropped_filedir memory
 				break;
 			case SDL_QUIT:
diff --git a/src/w_wad.h b/src/w_wad.h
index cd8ed1250..3780eddce 100644
--- a/src/w_wad.h
+++ b/src/w_wad.h
@@ -131,6 +131,7 @@ struct wadfile_t
 
 	boolean important; // also network - !W_VerifyNMUSlumps
 	boolean compatmode;
+	boolean localfile;
 };
 
 typedef enum wadcompat