Help with managing duplicate image filenames

Hello everyone,

I configured Picard to embed the front image into the music files, and save all album-related images to the images/ subfolder.
I selected all type of images in the Cover Art Archive settings, and my filename pattern for images is:

images/%albumartist%_%album%_%coverart_maintype%

I also configured File Naming options to replace spaces with underscores, but when an album has more than one image with a given %coverart_maintype%, the resulting filename is the same, so (1) is appended to the file.

How can I replace this with something like _alt1?
Do I just need to tweak the filename pattern or do I have to make a script that runs after the files are saved?

Thank you in advance.