Edit Sub Assembly

I've looked high and low in the API for a way to edit sub assembly. While probably not enough, hopefully one of you could make my search easier.

I don't see an option to edit a sub assembly. The options I do see are:

1. Editing a part from IAssembly.editpart2

2. Editing the top level assembly from IAssembly.editassembly

I do not see how to edit a sub assembly while in the context of a higher level size assembly. When you call editpart2 on a selected assembly it returns back -1, meaning failure.

I am sure there is a way, but my 2 hour+ search for the function I want has provided no solution.

Any help is appreciated.

SolidworksApi macros