with the swicthing jack i show on the schem/layout, you can use the amp as a combo by removing the plug and reconnecting the speakers. no dummy plug needed.
as for the mid control, what i did was remove input 2 and moved the volume to to that hole, and rewired a mid control in the tone controls by sliding the bass knob where the volume was and placing the mid control where the bass was. this way when used as a combo the only function i lost was the use of input 2, which i never use.
"The process of selecting the tone on the guitar is an aesthetic process like any other, so you try a lot of different things. Most of the things I’ve tried I’ve tried in live performances" ~ Jerry Garcia