I have set up my global admin with the same address as my on prem AD account. I created a minimal hybrid environment also using this same Global Admin account. Now that I have used AD sync to bring in my on prem accounts, my local AD account is listed along with the duplicate Global Admin. Can I rename the global admin account without breaking the hybrid exchange setup that I used the credentials with? @apala56
As with any "rename" operation, if you are changing the UPN you will potentially have to update any stored credentials used by this account. For the purposes of minimal Hybrid or AAD Connect, it shouldn't matter though.