[abdessamad idrissi]

I think the correct way to add tags is by a plugin, normally you should never edit the core code of bbpress! because if you do, next time you update your bbpress you will be deleting the modified core files, then you will get trouble with your forum not working properly.. So the best is to use a plugin for things that deal with core files..

PS: Core files are files that are not Themes nor plugins, such as files under; bb-includes and bb-admin,