Yes SBR carrier can be used for attaining the same authenticatriong user functionality like SBR enterprise aslong as the radius process is up & running along with active licenses loaded on the existing server.
It should not be a problem however please ensure you have an supported SBRC version if you need to get any support from Juniper support team etc once you implement this production.
SBRC end of life/End of support information can be accessed from the below URL.
You cannot convert SBR-C instance to a SBR-E instance. They are not compatible. Especially with SBR-C 7.X and above, the Carrier code and Enterprise code have siginificant diffrences and any kind of migration is not supported.
Why do you want to convert from Carrier to Enterprise edition. I can't think of any feature that you could use in Enterprise which is not available in Carrier.