Hi Andrew,
Product manager for Perform (competencies) here. It is currently not possible to have multiple scales for a framework, but I'm interested in learning why you're needing this capability? Can you please provide an example or scenario where different scales would be appropriate?
We have a feature request space in community, https://totara.community/totara/dashboard/index.php?id=105, where you can browse existing feature requests and add this request to the list. If one already exists, you can upvote the request, which lets us (product team) get a sense of the importance and urgency of the feature.
Cheers,
Ashley