https://blog.novacare.no/episerver-tinymce-settings-attribute/ allows you to achieve b I believe. I checked and this OnMetadataCreated runs every time it's loaded so you can put a group check in this method and dynmically set the property to whatever you want.
Did this solve your issue Ethan?
I need to restrict the markup button in the MCE. Can I:
a) Set permissions on specific buttons in the MCE
b) Can I load different Tiny MCE profiles based on user roles?