If it was a M1 Garand or a 1903A3/A4, I would agree. However we are talking about a "cheap" Mosin. You wont hurt the value by doing so...
A guy I know takes "cheap" Roman 2000 yr old coins, drill holes in them and uses them for tags for his sheep.
Cheap coins? Yes, but he has just destroyed a piece of history that cannot be replaced.
Our grandchildren or greatgrandchildren will be scrambling looking for original MN rifles that have not been altered. We are custodians of history and it is our job to preserve it for future generations .
Especially military rifles that represent important times in human history.
I am not against simply taking the stock off and putting on a synthetic stock, that can be reversed.
But when you chop the barrel and drill for a scope, you have changed the weapon forever.
Again, just my .02 cents.