Shortening Original Forced Air Runs in unfinished room.

Going to be finishing a room that is approximately 300 sq ft. The original forced air runs terminate/exit approximately in the middle of the room in the basement ceiling (floor joist cavity). I would like to move them by shortening such to free up some joist cavity room to put lighting/speakers etc. From memory will be shortening two runs that supply that room each by maybe 7 feet. Is this advisable or is there any technical reason why one should/cannot.

Thanks much!
Theeld

source https://hvac-talk.com/vbb/showthread.php?2226815-Shortening-Original-Forced-Air-Runs-in-unfinished-room&goto=newpost