Can we flash Zaurus SL-B500 (Japanese) with SL-5600 ROM?

Hi,

My friend has a Zaurus SL-B500 (Japanese version) and he would like (if
possible) to convert it into an English Zaurus. As it has same hardware as
SL-5600, CMIIW, I am thinking of flashing the ROM using SL-5600 ROM. Is
this possible?

I've tried to browse internet to find answer to this and from what I could
gathered, what people do is changing the menu to English but do not flash
the ROM. I couldn't find any reason why they're not just flashing it.

Any hints, suggestions, link to sites that cover this would be appreciated.

Many thanks,
Zuki