Didn't MTM "give" the jingles to WKRC to head off any legal action due to WKRP being only one call letter different and easily mistaken for WKRC. I doubt the FCC would at the time approve WKRP in the Cincinnati market with WKRC all ready in the market. Also the mythical station was in the low dial position 500's too.
What 55KRC did was over dub WKRC over WKRP with a lady's voice from the office. There was a lady in the office who had a nice singing voice and they had her sing with the TV theme song.. I have a copy of it. I'll try to get it up on the web and give you the link.