Backup your database, either Save As Smaller or Save Clone.
Open the Backup, Delete everything on Main Old and copy paste everything on Main New.
Any fields that are common to the two layouts will have data, any fields that are not in the Table that is displayed on the layout will have to be adjusted.
All scripts should work if the new layout format.
A layout is an object in the database and the relevant scripts point to that particular layout.
Backup your database regularly, especially when editing the design.