Mods without being the host?

If i load a mod on my computer shouldnt it atleast load on my computer when i join a game or is the host in charge of everything? and is that why hacks exist?
and in that case what is the difrence of coding a gsc mod and a hack, how long can you push the limits in a hack?

Thanks

Sorry bad english

I think you cant use .GSC if your not host.

Yea finally someone answered. Thanks

No else has answered this, so all i can assume is that it's true, but how would you use .gsc in say... a dedicated server?