regarding BEagles question, it happens- while in my early stages I witnessed a student land with 1800 rpm in a c152 (not by choice). He used flap, and carb heat to fly the initial approach to the ground (long runway) then mixture to stop the aircraft.
And while not quite the same I had a throttle linkage fail (un bolt) on a C337, resulting in the rear engine "stuck" at 75%. In my case I went around. flew the circuit on that engine with gear and flap extended and the other engine at idle, then once assured of a landing I shut down the 75% with the mixture and used the other engine to make a normal landing. Turns out someone had not used nyloc nuts where they should have.