Freeze! Don’t touch anything. We are migrating. (Still???)
Yikes! Luckily business users are extremely adept at finding work-arounds, often when you don’t want them to. At the end of the day though, migration can cause productivity woes until the migration of content can be validated. Unfortunately another pot hole in the road to a successful migration, typically causing unexpected delays.
A rather different approach that we recommend is to essentially pre-process the content to be migrated. This eliminates, or certainly decreases the issues that can be caused that prevent business users from using the migrated content. During migration, you are then confident of the end results. This pre-processing step includes metadata analysis, auto-classifying content to a taxonomy that will represent how content is classified when migrated. This enables the elimination of several issues that prevent an on-time, on-budget, and overall a successful migration. A side benefit is the beginning of an enterprise metadata repository that will achieve other benefits such as improving search after the migration.