Can I be added to an existing conventional mortgage on a home?

[Matt Wells]

Can I be added to an existing conventional mortgage on a primary residence? For example, say I own 50% of a home, but my name is not on the title or mortgage. It's all in another person's name. Can I be added to the title and the Fannie Mae/Freddie Mac mortgage loan at a later date? Can someone please explain how I can do this if it's possible?