Change AD/LDAP Domain

Hello everyone,

we have an UCS 5.0-8 errata1168 with a fake domain ( pahl.intranet ) and im thinking on changing that to int.name.tld or ad.name.tld.

So i can only have one ldap domain on a ucs what is the right way with less work?

Setting up a new UCS with the new Domain?
Changing configuration of the existing UCS?

We have one main office and three branch offices which are connected by site2site vpn with tplink omada hardware. Sadly they can offer dhcp server but no dns server.

Per office its only 2-4 Windows Computer which RDP to a RDS Server in the main office.

So what is the best practice here?