If they have been subjected to reverse polarity, then they will have been damaged internally to some extent. Obviously, this depends heavily on the voltage level, temperature reached and time applied and those are all completely unknown quantities but, since he's doing this for someone else, it would be a shame for the electros to fail... let's say "early"... when, for a few cents/pennies each, they could be replaced and therefore relied upon. Resetting the clock, I suppose, given that they are "lifed" items.
If it was my pedal or I was doing it for money, or even if I was not being paid but there's no guarantee that the chap won't move away from my town, then I'd do it. They're cheap as chips, so why not?