How to add a province to a faction at the start of a game?

[roman dude]

Hello, I was wondering how I could add a province to a faction so that it controls it at the start of a game. For example, I would like to add Kophen to Baktria.

And one more question, how can I add buildings to cities? Like if I wanted to add some buildings to Kophen so they would be there at the start. Thanks!

Edit: Is it just really complicated to do or not possible? I would appreciate some info on it, I promise I won't bother anyone about it anymore...