If a user has a personalization for an existing form in Epicor, and you create a new customization, as soon as you "deploy" the customization by linking it to the form in Menu Maintenance, the user's personalization will be ignored.
Personalizations are always based on either the default form, or a customization (referred to as the parent layer).
To hook the personalization to the new customization you must:
1. Export the personalization to an .xml file by either:
a) Using System Maintenance, Utilities, Customization Maintenance (sic)
b) As the user, open the personalization designer, and choose Export button.
2. Attach the new customization to the menu.
3. As the user, log into Epicor, open the form (customization should now be loaded), start personalization, and click Import button.
Note that the only way associate the personalization being importing to the new customization is to log in as the user. You can not do this from any other account.
That said, Epicor does not recommend re-importing personalizations under a different customization. Instead, they suggest the user should recreate the personalization, because moving the personalization to the new customization may yield unexpected results. This is because part of the user's personalization is not actually exported to the personalization xml file, but instead is saved locally on the user's computer (such as the location of certain grids).