In a nutshell:
Change absolutely nothing on the existing rental unit. Not one single thing. Then enter the other unit as a physically separate property.
If you need detailed help on this, then I need to know how you've been doing things for the existing rental unit.
Treating the rented unit as a physically separate asset with 100% rental use and just claiming 50% of the expenses? Or treating the unit as a 50% unit where you enter 100% of the entire building expenses and let the program "do the math" to figure what percentage of those expenses to apply to the SCH E?
The more details and facts, the better.
