Script that renames filenames in folders.

I am looking for a script that can rename filenames in my folders. The current naming convention of the files is descriptive names. I do not have a preference for the programming language used for the script. The new names should be a combination of the old name and new information.

The files are scans of photographs, front side is one file, and backside is one file. They have the exact same name, except that A is front and B is back, and they is the last letter in the file name. Example:
TTKK_IND_mmA.jpg
TTKK_IND_mmB.jpg

We need to be able to run this on a folder..and all the under folders in that folder... and the script should SWAP the last letter. So if it is A..it should be B...and if it is B it should be A.
The Front and back are wrong on the files, so we need to flip them.

We could have the source folder fixed i the script such as C:\SCAN\incoming\
so all the files in that folder will be affected when we run the script..and then we move the files from that and insert the next batch.

I need this ASAP:

Ideal skills and experience for the job:
- Experience in scripting and file renaming
- Proficiency in Python and/or JavaScript
- Attention to detail for accurate renaming
- Ability to work efficiently and meet deadlines