Thank you for posting here.
Here are the answer for your references.
According to your description, my understanding is that you have a single active directory with 2 domain controller(Assuming the names are DC1 and DC2)，and the two DCs are in the same site (assuming the name is Site1).
Now 100 systems are operating normally in the subnet segment divided by Site1. You want to build another site (let us say it’s called Site2) later after 6 months and you want to move DC2 to Site2.
Do you want to move 50 of the 100 existing systems to Site2 where DC2 is located, or do you want to create 50 new systems for DC2 and add 50 more systems after six months? No matter what your situation is, please confirm the following information:
- Check if AD environment is healthy. Check whether all DCs in this domain is working fine by running Dcdiag /v on each DC.
- Check if AD replication works properly by running repadmin /showrepl and repadmin /replsum on each DC.
- Check both SYSVOL folder and Netlogon folder are shared by running net share on each DC.
- Check we can update gpupdate /force on each DC successfully.
The following is a response to your question:
Q1: What is the impact with respect to group policy, password change etc?
A1: If your sites or DCs are physically separated, you need to ensure that the VPN you have to establish a VPN connection between those sites.
If your sites or DCs are in the same domain physical location, there will be no problems.
Follow the above step1-step4 to check, if everything is normal, the operation will not affect the problem you mentioned.
Q2: After moving the 2nd DC to site will they get sync properly?
A2: In response to this problem, after moving the 2nd DC to site, you can run repadmin /syncall /AdeP and gpupdate /force on the two DCs to force AD replication synchronization.
If all DCs get sync after running repadmin /syncall /AdeP, we can follow step1-step4 to check AD environment again. If everything is normal after checking, it means AD is working fine.
Hope the information is helpful. If anything is unclear, please feel free to let us know.