I'm answering you here since I think your question at the discogs script topic is not releated specially to this script, right?
What you propose there is not possible with mp3tag. You can't combine .src files like you can combine actions to action groups. You would have to run every script for every tag for it's own, so you would run about 15 scripts for one album!
But you can reuse command blocks in other scripts. Just copy them and insert them into your own script.
The only tricky thing is that the new script finds the right place in the web source where the comand block is belonging.