By the way, regarding "why do they format IM" mistery, the code for "format internal memory" inside the UI does the following:
set exit code to -3
restart
Bittergourd
You can put prsp.sh file into /database/system/PRSPlus folder, it's content gets executed on reader startup, (but only if the reader is not connected via USB, this allows one to "unbrick" from broken script situations).
To replace default fonts one could use "chinese" way:
1) Put the new fonts into /fonts folder in the internal memory (you can actually use any folder name /something/somethingelse/blabla would also work, just change the script accordingly).
2) Put prsp.sh file, containing the following line (/Data is the path to the root of internal memory):
mount --bind /Data/fonts /opt/sony/ebook/FONT
NOTE:
a) usual font restrictions still apply: i.e. file names, font names
b) if you decide to change fonts in /fonts folder, don't forget to remove the "mount" statement and reboot first (Internal memory access via USB is already buggy, God knows what files will get corrupted if you will try to overwrite locked files)
c) watch out for windows style eols (\r\n - wrong, \n - right)
d) if something goes wrong, don't worry, simply reset the reader and quickly connect it to USB, prsp.sh will not get executed
Hope this helps.