Don't you mean "match the first 8 characters but ignore everything else after that"?

I assume by source you mean the source for the -tagsFromFile option.

For this to work, you must be able to generate either the source or destination filename _exactly_. If the "anything" characters are different in each case, then this can't currently be done. If you can construct the source filename exactly then it is easy as you point out. If you can't do this but you can construct the destination filename exactly from the source filename, then it is a bit more complicated but you could use the -srcfile option to do this.

Otherwise you need to write your own script to make the associations you want.

Sorry, but exiftool doesn't have the ability to specify wildcards in the -tagsFromFile argument.

- Phil