I have seen a lot of posts about renaming repliation groups that state that there is no way to rename your replication group. I was able to rename a replication group by using ADSI Edit (adsiedit.msc). Here is the method I used:
Open adsiedit.msc on one of you domain controllers, expand the top-level 'Domain' tree, expand CN=System, expand CN=DFSR-GlobalSettings, right-click CN=[replication group name], select 'Rename', change the name to CN=[new replication group name], expand CN=[new replication group name] and check to make sure that all child objects are using the new name.
Once the change is made you may received some errors while the changes are replicated throughout your network, but eventually it will all sync back up. At least it did for me.
P.S. - Please be careful using the ADSI Edit utility as you can corrupt your Active Directory configuration by changing the values incorrectly. I suggest you test the changes in development before deploying to production.