This is always my fear when I do the internet pre-paid room. "Now that we have your money and aren't giving it back, bend over..."
So, if I'm going to arrive late, I always note that in the comments along with "so please save my king, non-smoking bed." If it's big convention-type hotel (vs. your run of the mill W or Westin), I'll even call during the day and speak to someone at the front desk to "confirm" my reservation, at which point I confirm the king, non-smoking part, and inform them of the hour I'll arrive and how much I appreciate them holding my room. Sometimes the front desk agent offers to assign and hold me a specific room and/or quasi-check me in right there over the phone.
This system has worked all but once--at a Marriott!
