Assuming that the soprano strings are of smaller gages than the concert (not always true and not sure about Aquilas because I don't use them much) then the tension should go down some. That said, there are three possible problems with doing so:
1) Intonation up the neck may not be as good with the lighter gage strings. But it could be okay or even better - lots of variables so you basically just have to try it and see what happens; I've been pleasantly surprised a time or two when strings I expected not to intonate well on a uke actually intonated better than the stock strings.
2) You will almost certainly lose some volume and sustain.
3) You may pick up buzzing for two reasons. First, the lower tension allows the string to vibrate in a bigger arc so it may hit the frets. Second, the thinner strings (again, assuming that the soprano strings are a lighter gage) may sit deeper in the slots in the nut, putting them closer to the frets on open strings.
4) In addition to the probable loss of volume the "slack" strings may also sound different, have a different timbre. This isn't necessarily bad but you should be aware of it.
Finally, tension on a properly set up concert isn't really that high - only very marginally higher than a soprano. If you're wanting lighter strings because you're having trouble with barred chords near the nut (Bb, especially) then chances are the nut slots are high and if that is the case intonation at the first couple of frets isn't going to be that great no matter what strings you put on it. In the long run it is probably better to fix any problems like that than to mess with the "voice" of the concert by going to floppy strings. Just my $0.02 - some folks actually like floppy strings - me, I'm running hard strings on my sopranos...
John