yes you can......Go to your game folder ( cstrike/ or hl2mp etc ) then open up gameinfo.txt and then look for the line:
ToolsAppId 211
change ToolsAppId into something like: FoolsappId, just something else doesn't matter what. And, omgomgomgomg, there ya go it works! But now the source sdk won't work, so to use the sdk change it back into ToolsAppId.