Can we add new 3d interiour rooms

[Gotmilk]

Hi. I have 3 years of experience in 3d modelling. So its not a very hard task for me to model a 3d interior. I would really like to add captains cabin into the sub. A place where you can hang out and write down your logs.

So my question is. Is this even possible. Lets say i model low poly 3d cabin. Is there a way someone could add this into a game and make it so that we could put camera into it.

Thanks.