Is there any way to copy one tag from FileA to another tag (different tag) in FileB?
See -TagsFromFile option (https://exiftool.org/exiftool_pod.html#tagsFromFile-SRCFILE-or-FMT) paragraph four and Copying Examples (https://exiftool.org/exiftool_pod.html#COPYING-EXAMPLES)
Basically, for a single tag
exiftool -TagsFromFile FileA "-TAG_B<TAG_A" FileB