Hi Fabio and
to the forum.
The stator in the 72V motor has different windings to the 48V motor but it will run fine on 48V.
The main disadvantage with running a 72V motor on 48V will be that the maximum speed will be reduced by a third, so you'll only reach 2,839 rpm @ 48V instead of 4,259 rpm @ 72V.
If the controller can be set to run on 48V, and you are happy to accept a much lower top speed as well as reduced power, then running your 72V motor on 48V should not be a problem.
Alan