If you search antique-locks for “Schwab” (upper-right corner) there are 8 other threads on Schwab safes, some have useful images (I hope). For example:

In this case the lock has a small round access “portal” near the middle of the door which would make this easier but then we see there is a second (locking?) door right behind it, plus some shelving, both of which would make access from the back much more difficult.
In another case:

It looks like there is no convenient access to this lock without removing the entire interior panel of the door which is probably not possible from the back with the door closed. This safe also has shelving.
Knowing how your safe is laid out will greatly ease your task of access by drilling/cutting the back, or maybe I should say it will be slightly less impossible?