Hi Sergey,
Absolutely! I'd be happy if I could mount a YOUTH or BANTAM stock from an 870 or 500 at this point.
The problem with the PM5 right now isn't necessarily the LOP being 13.5", it's the 13.5" LOP, plus the fact that the forend is located extremely far forward; nothing can be done about the forend, but, 2" chopped off the stock (for a 11.5" LOP) would go a long way for making a much better handling shotgun.
Easier solution perhaps... find a way to chop the stock 2" shorter and attache a new buttpad (or reuse the original somehow)?
I'd be up for that service if it looked factory.