Data stored in credentials does not have to be only for sensitive information.
The other template tags in the settings are defaulted configuration for operation, but the handle & instance seem to be data for the user’s account, which are data for use in authentication, and so even fit within the general description for the intended purpose of credentials.
Credentials are service tokens and authentication information stored by Drafts for reuse.
If you included them as credential data, you could then prompt for it on first run. Switching accounts I think (I have not fully worked through the code required) should then come down to having the actions written to reference accessing a particular named set of credentials.
Just a suggestion in the hope that it might save you some future headaches.