Adding New Project Type Class??

Is it possible to add a new Project Type Class, as an addition to the currently 3 seeded types - Indirect, Contract, and Capital?     Are there any pluses/minuses to creating a new type class?  

This essentially would be done to differentiate indirect projects that are burdened from those that are not burdened at a higher level (type class) as opposed to at the project type level.  

Thanks in advance.

Joe