Can you take a feathered stopped engine unfeather the prop to fine pitch and bring it up to full rpm and turn back on the fuel or mags (which ever was off) I am thinking not.
As I said in a previous post: yes, you can.
Even heard of attempts on the ground by turbo-prop and jet - understand the jet attempt ended in tears in fleet manager's office
Re the manifold pressure Q: forty something years ago I could have tried it for real to see exactly what the change was but no Varsities left flying.