Autodesk Revit MEP

[#1]

I am doing an electrical design project on an existing building.  

Does anybody have a good strategy for assigning/estimating the existing electrical loads?

Is there anyway to do some sort of hybrid panel schedule that will accept manual input and modeled loads.

[#2]

If you are not concerned with the load classifications, you can assign a Spare along with a name and load. Otherwise, I would suggest creating an "Existing Load" Family and assign it to a Category that you do not use and can keep turned off (i.e. Site). Draw a box and put an electrical connector on it, and make Voltage, Number of Poles, etc. Instance parameters. Place one instance of this family to simulate one existing load.