Manually manipulating admin.users collection? what is safe?

I’m maintaining a number of small mongo instances with common user base on them. It would be ideal to be able to duplicate user access/credentials between multiple instances instead of using the db.createUser/db.grantRolesToUser functions.

Is there any information on what could safely be modified directly and if so, what actions need to be taken after the fact if any? (i.e. w/ mysql a ‘flush privileges’ call)

Example A) Taking the entire admin.users collection and loading as-is onto another instance.
Example B) Adding user with above calls, but with a scrambled credential - and then post-updating the document for user with a replacement set of SCRAM-SHA-X objects copied from other instance or generated offline?

In case it matters, this is with a 5.0.x community edition install.