Well, it seems you can, but it's no easy matter and even risks bricking the device!
https://www.mobileread.com/forums/sho...=168282&page=3
Coolreader does not pick up the fonts in the sdcard\fonts folder, and it is very difficult to write fonts to \system\fonts which coolreader will see. See the link above. It's not easy.
Fbreader will accept custom fonts in sdcard\fonts, but it does not recognize the sony page turn buttons.
The bottom line is, there is no good ereading app for the Sony T1 (if you want custom fonts and page turn buttons).
The solution is...use the existing Sony reading software (compile the epub with css just like with a 650). So for me rooting offers no improvement for reading books on the Sony T1.
I'm surprised. Rooting is pointless for reading normal books. It offers no improvement.