Not sure, it is a PM and so you can't carry that much so less likely than the GM. I saw someone using it this way with the MM on youtube. I would say proceed at your own risk, if you see any signs that it is causing a problem then stop. For me, I don't intentionally try to damage my bags, but I want to get the most use out of them and if it means that I will carry it more this way compared to leaving it alone and not carrying it because it is less convenient, then I would just make my alterations and enjoy the bag. If it get's damaged then I cross that bridge when I get to it. But this is just my personal opinion. I carry my Neverfull PMs much more often now with the strap and I am happy to be using them. They are holding up well and I have not seen any damage, same with the alteration to my speedy.
All the best!