Case insensitive metadata with regular expressions

For some unknown reason files I’m dealing with are named inconsistently. For example, filenames of images from the same well and FOV are lower case for some channels but uppercase for other:
Staining1: expname_a01_f01_c2.tiff

Both images should be assigned to Well=A01 and Field=01. However, when I’m extracting metadata from filenames using regexp, I’m ending up with two separate entries for Well field: A01 and a01. This obviously isn’t good, results in mismatched images in NamesAndTypes module and generates nan’s in Groups module.

One solution would be to batch rename all files to lower or upper cases but for technical reasons it’s not possible without copying files (no write permissions on the server where images are stored).

I noticed ‘case insensitive matching’ in Metadata module when importing metadata from file but is there a way to assign metadata regardless of the case using regular expressions?