Product Managers are among the most important --and influencing stakeholders in a migration project. Actually, they are the “owners” of the application that is being migrated and because of this, they may be reluctant to approve changes to the application.
In many cases, it will not be possible to reach the state of Functional Equivalence in a target platform with 100% the same user interface features as the original application. For example, Tab Controls in Visual Basic 6.0 don’t respond to click events when they are disabled, so the user cannot see the contents of the tab. In Visual Basic .NET, tab controls still respond to click events when they are disabled, so they display their contents in a disabled state. This visual difference is intrinsic to the way the .NET control behaves, and therefore it should be regarded as an expected change after the migration.
Just like the one I mentioned, there may be several changes in the application as part of the migration process. It is very important to make Product Managers aware of these expected changes, and have their approval before the changes are made. Product Managers will have great degree of influence on your migration project, so do your best to keep them on your side!