Dear Kornrade,
Unfortunately your study appears to be incorrect, because there is at least one alternative solution:
1.Bh3 gxh3 2.a4 h2 3.a5 h1=Q 4.Nexf3 Qxg1+ (first variation of your solution)

and now 5. Kxg1 bxa5 6.b6 a4 7.Ne5 a3 8.Ng6 a2 9.Ne7#

A faster mate without touching the g-pawn. Guess you must do some repair work before publishing it...

You are right about that variation, but...
The toughest defense by Black, and the proper way of rendering the solution is:
1.Bh3 gxh3 2.a4 h2 3.a5 bxa5 4.g4
4... h1=Q 5.Nxf3 Qxg1 6.Nxg1 {on any queen move, white captures}
4... h1=N+ 5.Kxf3 Nxg3 6.Kxg3 {on any knight move, white captures}
4... hxg1=Q+ 5.Kxg1 f2+ 6.Kxf2
==== these moves could be placed everywhere in the solution ====
6... a4 7.g5 a3 8.g6 a2 9.g7 b6 10.g8=Q+ Kb7 11.Qb1#

Putting the solution this way, it is clear that all options lead to a mate in 11. The problem does not need to be changed, I just needed to be a little more attentive in writing the solution.
Thank you for pointing out the inaccuracy.

Well Kornrade,

you are right. The solution was wrong, the position is ok. Just checked it