MyBB Community Forums

IS there a plugin that you can use to change the header for each category OR forum you go into:

For example:
The Category CARS, when you go into the category, the header changes ( mostly only the logo & favicon too)

The reason why Im asking is because im buying multiple domain names & I just want the domain names to be redirected to specific categories that way people can switch between different domains while still logged into the same account instead of having different entities ( ie. 2 seperate forums for totally different things)

You may be able to do this through the use of separate themes for each forum. I agree that it may not be particularly desirable though, especially if you want users to be able to select their own theme.
Another possibility, depending on how much you want the header to change is to use the forum rules and modify templates to get it to appear in the header.

Can I use seperate themes for each forum~? Is it possible~? If so, is there a plugin for it~?

Can't you already do that? I was pretty sure you can from the ACP, under advanced options. (When editing a forum)

Holy crap I didnt know that... Im gonna check it out right now, brb