When a company is acquired by another company or the two gets merged, then two different business units come together to function. After acquiring the company, your boss asks to rename the acquired infrastructure(Domain/Website etc.) according to the current company standard, but renaming the internal AD domain is not as easy as it looks. When number of in-house and 3rd party applications are involved, it is difficult to rename the AD domain according to your choice. Few more impossible scenario exist where you can’t rename the domain such as environment running Exchange 2007 and above or CA services. The viable approach is migrating complete environment using migration tools like ADMT/Quest/Netiq etc. which is safe and recommended approach. Migration is a complex process, but it is a better approach then jeopardizing the whole environment by performing domain rename.
Domain rename is not a full proof option. After reading across various forum and posts, i found that people faced various issues or completely broken their environment after performing domain rename. So, whats next after domain rename disaster. The only option available to them is to recreate the new forest & start everything from scratch.
The best way to handle acquisitions or merger is to migrate everything from the newly acquired company to your own domain or in new forest. The chances of breakdown is less in comparison to the domain rename success rate. Migration itself is not easy, but careful planning & consultant can make it a better option.
Take a look at below guide from MS on Restructuring Active Directory Domains Between Forests.