Can these actually be made into libraries accessible from ROMs, eg PCEmon, a hacked TenNoKoe Bank ROM, etc?
I don't think that I quite understand the question?
These
are libraries, distributed as "C" source.
You just include them in your CC65 project, decide what code/data segments/banks you want to put them in ... and use them.
CC65 doesn't really impose any limitations on where you choose to place stuff ... it is entirely flexible.
With CC65/CA65, it's easy to mix "C" and assembly code ... so you just write your ROM in whichever language makes you happy.
I still need to finish-off low-level SD-card access functions ... the one's that Mooz did for the TED1 have needed a fair bit of fiddling about to get them even partially-working on the TED2.
I can't see them being much use for hacking into the TenNoKoe Bank ROM. Instead, I'd rather assume that anyone wanting to copy data from Backup Memory to SD card would just write a completely new ROM.
If you're thinking about an expanded Super System Card with something like PCEMon and copying Backup Memory to/from SD card, saving screen grabs on SD card, etc ... then "yes", I'd say that it is certainly possible.
Something along those lines is one of my goals, with the TED2 System Card patch as a 1st-step.
The TED2's built-in USB connection to a PC makes things even easier and more convenient for people.