I found mySpire, for those who don't know it, it's supposed to edit the boot images for a unique calculator experience.

Sadly, this only works on 3.1 as stated on https://ndless-apps.org/

However it does start on 4.0.3.29 and i can successfully edit /phoenix/manuf.dat
The changes remain active until i reboot the calculator (reboot / crash doesn't matter)

How comes the manuf.dat file gets refreshed on every boot?

Also is there anyone able to build mySpire for 4.0.3.29?
I have hardware revision J, might that be the problem?