I use manual users in the first testing, then go over to users synched in from ASM and Entra ID authentication in production. The manually created users are usually either taken out of use when turning on Entra ID authentication, or already have working Entra ID user credentials. Anyway, already enrolled devices will remain enrolled, and retain the linked user as long as it exist.
I would try to do the user change/turning on Entra ID authentication over the summer, and do a full reset of all devices to ensure all are enrolled using Entra ID authentication after the summer.
And, for covering your rear end, like @Greg says, contact your local Jamf sales engineer/Jamf Support to confirm the solution is viable and supported before putting into production.
