Howdy,
I am a little short on cash at the moment so I had the idea of recording over some now-useless footage I have on some Panasonic Professional AY-DVM63PQ Tapes. They have been recorded on once before.

My question is, would it be okay to record once more onto these tapes?

yes, it is. If they only have 1 pass on them you should be fine.

Okay, thanks.