From a quick test .... if you are already playing something when the alarm time is reached then the alarm is skipped.

At the moment I try to tune in to a radio station for particular news programmes.
So - for example - I would set an alarm for BBC Radio 4 at 17:00 Monday-Friday.

If there was a setting for each alarm that had an "interrupt current output" (can't think of the right wording) then it could see if there is something playing at present ... Pause ... put the alarm at the Now Playlist slot (shuffle everything else down by 1) and Resume.

If it is a playlist that is scheduled then I guess it has to replace the current playlist as a whole.

Then at the end of the alarm duration (which would be the programme length in my case) it would move to next item in playlist.
If I have heard enough of the news then I simply hit Next to get back to what I was listening to before (with that track restarting).

Alternative approach would be to put it as the Play Next item and then do a Next

Alarm could skip if the scheduled item is the same as is already playing.

I have not looked at the code yet but am willing to give it a try. Wanted to get some feedback first.