I do not have a machine to try, therefore my question is
what if I program a part in Mastercam with cutter compensation set to Computer, however the operator uses cutter compensation in Control.
Would there be an alarm on the CNC because it cannot find a G41/G42/G40
The cutter comp will not work unless you send the G41,g42 code. Computer comp uses your tool cutter diameter and does not send the G41,42, so if you are using a .5 endmill that is under size change the tool diameter and the toolpath will change. If the operator programs tool diameter offsets they will not work unless the G41,G42 are in the program. Best thing is to avoid cutter comp unless you are running a very new Fanuc, Haas control. The older controls are a nightmare sometimes and the lead in waists alot of time.