@Salves You can install the AAD connect on any other member server. But you have to make sure that you do all the customization regarding sync rules and Filtering exactly same that was configured on other server to make sure you do not cause any alternations in sync or to already synced users/groups.
If you do everything similar to the previous AAD connect config, all the objects will start syncing from new AAD connect setup and will have no issues.
For future, you can also have a Staging server which is beneficial in a scenario like this : https://learn.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-staging-server
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