Q. When a client licenses a track for commercial use on television, is it permitted to edit the track, make a loop with it, or sing on top of it?
A. These are really three different questions in one.
Regarding the question about editing and looping a track, you are permitted to edit the track as necessary for your production, whether for television or any other type of production. This includes cropping, looping, lengthening (i.e. time-expanding), shortening (time-contracting), pitch adjusting, adding effects such as reverb, echo or anything else.
Regarding the last part of the question about whether you can sing on top of a music track purchased at AudioSparx, please see this article here.