Why not rename just by pressing enter with the layer selected?
I don't know of a way to turn a solid into a null, but you can make your solid a guide layer so that it won't render.
ctrl-shift-null is the shortcut for bringing up solid options. Not for renaming.
There is no way to do what you're asking to do.
I have always thought that adding 100 x 100 solids to the project panel when you create a null was a waste of time. Here is what I do: create a null using the keyboard shortcut (Find it in the menu) then press the enter key and rename the null in the timeline and you're done. IMHO adding a null should be like adding a shape layer. Nulls should live in the timeline, just like shape layers, and not in the project panel.