there is a document on how we currently handle disputed borders: http://www.osmfoundation.org/w/images/d/d8/DisputedTerritoriesInformation.pdf

There are some discussions on the tagging of disputed borders, see the tagging mailing list threads:

I think is it better to avoid editing borders of countries without talking to the communities in all involved countries. Especially changing borders based on documents from one of the 2 claiming parties.