I think you can buy a tool that helps when rekeying these now?
Silca Prima

Cookson used to make the rekey jig but it has been out of production for a few years now, some of us have one though.
Paul C has a programme for them on his Prima, got to be the best way.
Chunk, any frustrations you may face when manipulating this open are just half the story if you are cutting a key by hand afterwards. You'll wish you did use explosive.
PS these safes were sold as explosive resistant too
