I tried applying the "Enable markup for sideloaded kepubs" patch from
this Elipsa thread for 4.29.18730 for my Sage, but I received the following error:
--> could not apply patch "Enable markup for sideloaded kepubs": line 1461: inst 2: ReplaceBytes: could not find specified bytes
Any tips? Or any type of testing that I can help with in resolving this?
The patch worked perfectly for the Elipsa itself when patching 4.28.17925, which hopefully rules out user error

and points to just a difference in the device and firmware.