Merges that have changed correct family information.

Is this within the family group or in public profiles?

Can you post a link to an example profile or tree and give specifics?

It's a bit complicated to undo merges. How complicated depends upon how many profiles were merged. You can post in the thread http://www.geni.com/discussions/80793 and at any time of the day or night, there will likely be someone who can help.

Look at the Revisions Tab to see who has been merging and editing.

You can "revert" edits and About Me edits but not merges. That takes going into the tree and creating a duplicate (since two profiles were merged) and then making sure that each of the profiles has the correct spouses, parents and offspring.

The best prevention for bad merges is well documented profiles with Sources attached, detailed Overviews, and even Master Profiles with locked fields, if the information is backed up reliable sources. Even then, bad merges happen.

If you have someone in your family group who consistently makes mistakes, you can remove them. But someone else could add them again. Educating people and communicating with them is the best method.