You can dissasemble the bolt.
Once you get the bolt face off, push the tip of the firing pin into a soft piece of wood.
Force down on the cocking handle to compress the spring.
Now you can rotate the rear knob of the bolt which will make the tip of the firing pin either protrude out from the bolt face more, or less if you turn it the opposite direction.
Be carefull though, you don't want it to pierce the primer or push it through the case, it could be bad news for you and your Mosin.
The general rule of thumb I use is, if the slotted disk in the center or the rear cocking knob is flush with the rest of the surface, I have never had a problem.
Are you sure you need to mess with it at all? What is it about the way the pin is striking the primer "too deep" as you say that makes you think it needs to be altered?
The mosin is a crude beast of a weapon Sir, it strikes hard.