SUMMARY
As https://unix.stackexchange.com/revisions/740698/4#:~:text=krename%20cannot%20do%20this.%20there%20is%20a%20sort%20of%20incomplete%20fork%20of%20thunar's%20renamer%2C%20made%20for%20kde%2C%20but%20which%20can%20be%20used%20separately%2C%20called%20%22bionic%20batch%20renamer%22).%20it%20lacks%20some%20basic%20options%20(remembering%20settings%2C%20re-arranging%20items%20in%20list explains, there does not appear to be a way to rename from the end of the file, despite `^` providing the opposite.

This forces me to utilize `$`, which overwrites the file extension.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 40
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.8.9-300.fc40.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 7600X 6-Core Processor
Memory: 30.5 GiB of RAM
Graphics Processor: AMD Radeon RX 5700
Manufacturer: ASRock
Product Name: X670E Taichi

ADDITIONAL INFORMATION
I'm using https://kojipkgs.fedoraproject.org//packages/krename/5.0.2/6.fc40/x86_64/krename-5.0.2-6.fc40.x86_64.rpm (from https://koji.fedoraproject.org/koji/rpminfo?rpmID=37344477) not 5.0.1.