Is porting to a different version of the firmware (like 1.01A,1.01C, etc.) as difficult as it is for a different camera model?
What I learned during my recent porting activities is, that it is not very difficult to port a different firmware version from an existing port of another firmware of the same camera.
I expect that only some addresses need to be changed.
If you take my code (btw: porting is not yet finished, I only worked on loader, boot.c and kbd.c) you should have a good starting point.
Download Firmware for 1.00c (which I am porting to).
Get CHDK-PT.
Look (first in loader files and in boot.c) for each address which is greater than 0xFF810000 and check that address in Firmware 1.00c with CHDK-PT. Save the found instruction code to a text file.
Than search in your Firmware version for the same piece of code. Probably it will be just some additional offset. But to be sure, please compare found Firmware functions with the used sub_FFxxxxxx_my functions in boot.c to have the correct instructions used in the functions.
btw: I only used CHDK-PT the way to save instruction sequences and load them into Notepad++ for comparison with my boot.c code. Maybe CHDK-PT has much more power to do some work for you? Waterwingz will know more about CHDK-PT usage.
Maybe it is also useful if you compare stubs_entry.S from 1.00c with your firmware's version.
As I am not much experienced with these activites maybe someone else can give additional tipps which can save you some more time?