Surely, even under a RIS, if ATC tell me to turn/climb/decend then that is a clearance to do as told is it not? I accept you may have reason for not doing as asked and would duly inform ATC, but are saying that an instruction to turn/climb/decend is not a clearance to do as asked/told?
I have most definitely been cleared to land/roll/overshoot when under a RIS (internal aids or GCA), honest!
H Peacock