Just don’t do it.
From the article
When a company acquires another company, business unit, or product line, the purchasing company may also want to acquire corresponding IT assets from the seller. Specifically, the buyer may want to acquire some or all of the domain controllers that host the user accounts, computer accounts, or security groups that correspond to the business assets that are to be purchased. The only supported methods for the buyer to acquire the IT assets that are stored in the seller’s Active Directory forest are as follows:
- Acquire the only instance of the forest, including all domain controllers and directory data in the seller’s entire forest.
- Migrate the needed directory data from the seller’s forest or domains to one or more of the buyer’s domains. The target for such a migration may be an entirely new forest or one or more existing domains that are already deployed in the buyer’s forest. We recommend that you migrate the directory data without security identifier (SID) history. If you migrate the directory data with SID history, information about the seller’s forest will be retained in the new forest of the buyer. For more information about migrating directory data without SID history, see Migrating Accounts Without Using SID History (http://go.microsoft.com/fwlink/?LinkId=113694).
This isn’t just a so-so recommendation that may or may not be right for your specific circumstance (sort of like the disk configuration guidelines), this is a hard and fast rule. Seriously bad things can happen and likely will if you mess around with it. If you do it and run into issues, the DS Team at Microsoft will walk away shaking their head.
 They didn’t tell me this, I am just guessing based on my conversations with them.