We are in the process of helping a client move from a Legacy environment to new environment. Current scenario has a SharePoint Server with a few 100 thousand documents (Big govt. Agency). Now, we are provisioning the old users from old domain to the new domain using Remedy. Now, the question is..How do we make sure that the New Users created in place of old user has all the same rights on the documents. Note that the users are provisioned using Remedy and hence, no SID information is copied over. Rather these two users will be completely unrelated to each other. We should still be able to give complete permissions to the new user for the old documents.
Any way, by which we can map the old user SID to the new user automatically without using any migration tool etc. The only good thing is this entire scenario is..the Old User and the New User name will only be different by three characters. So if Old User was ABC, the new User will be NewABC.