Shouldn't have any issues at all once the trimfilm is in place and allowed to dry. I do this all the time for patched numbers.
Yeah.. You won't have a problem with that...
If you try to put a decal over an unused decal, the water will loosen / soften the underlying decal / paper and you'd likely have a mess on your hands..
... Dry Transfers however.. Do work (or so I hear).. I read on here someone trying to do dry transfer onto an uneven surface, and someone suggested applying to clear trim film.. turning it into a decal..
Also, If you had an Alps printer, you could print the lettering on the red trim film..
~Ian