How to increment calc value?

I’m, I’m a newbie with calc.
I’ve a 8 characters value in a colomn, that I’d like to increment from A to 9.
For example, let’s say I got R90AAAAA as a start.
How to get in the same colomn below R90AAAAA:

from third character to the last one (R9099999)?
If the file has more than 1000 lines, it’s better to split it in several files.
Hoping I was clear enough, thank you for your kind help!