Rename file extension (uppercase or lowercase)
When batch rename/rename is used it would be a welcome feature request to have an option to make the file extension capitalized, lowercase or change it entirely - this feature could find a spot in Preferences.
I often use Batch Rename and the one thing that I don't like is when I use List View or open up File Explorer some filenames have an uppercase extension and some have a lowercase extension ... but I'm not going to spend the time manually changing the extensions to match.
Stephen Marsh commented
In the meantime, you can use the following setup to change extensions to uppercase or lowercase.