the firing pin is no problem, Lothar Walther ( one member of the Walther family) made such inserts for the 22 lr rimfire

look here, it shoots 22 lr in a .357 mag revolver

https://www.tactical-dad.com/waffen/scharfe-waffen/einsteckl%C3%A4ufe-reduziersysteme/

you have a adapter cartridge with the dimensions of a 357 mag cartridge. between the rimfire cartridge and the breech is a firing pin adapter - rear end center fire, front end rimfire

I said it before, there was the 22 lr with center fire primer available between the wars. it was a 22 lr with an anvil inside like a boxer primer, works both ways rimfire and centerfire.
its not a good idea to have the 22 lr at the rear end because the bullet have a long way until it touch the rifling.

made a rough draft of the adapter you need, you recognice the .22 lr cartridge there?

take the measurments from your chamber cast and reduce by 0,1 mm, lathe turn the insert from steel.
make the firing pin from somewhat better steel quality so it don't wear off so quickly. you have to file the rimfire pin on the front end by hand. drill a little hole for the center fire fring pin on the rear end. I would lighten the firing pin on the lathe, you need the full diameter only on the ends.

the best way is an adapter like the one for the 7,5 Mas show here

the 22 lr cartridge protruding so the case mouth is in the barrel. this works as a gas seal similar to a Nagant revolver.

btw, never try to snap the extractor of the Mannlicher M 95 over a rim when the case is in the chamber. it will probably break what you don't want.