dont know exactly your Environment, but in normal cases this shlould be no problem as from the FIM perspective you only get some new attributes to the Schema (schema refresh!!) and maybe some new System Container.
Rember the PCNS if you use this for PW reset.
Edit: We have done this around 2 years ago by replacing the DCs with same Name and IP and didn't have any issues
Microsoft is conducting an online survey to understand your opinion of the Technet Web site. If you choose to participate, the online survey will be presented to you when you leave the Technet Web site.