-Student who has multi Commercial/insturment rating. If he/she want's to get Instrument prficiency Check, he/she can do this is a single engine? Or does he/she need to do this in multi?

-Helicopter commercial/insturment pilot wants to train single engint airplaine to get his/her instrument. Does the applicant must retake the written? Is it pretty much training all over again interms of requierments or does he/she get some sort of benefit on this training in terms of FAR/requierments?

Thanks!