figured this out, but im posting solution, as i really didnt understand any of the answers i found.
1. get your tables ready so that both the table you build first and the table you intend to switch the whole layout to are in your relationship manager.
2. go to relationship manager. change the name of the table occurrence of the NEW table to a temporary name.
3. change the name of your original (working) table occurrence to the name YOU WANT TO USE FOR YOUR NEW TABLE.
this will change the data source for all of the fields in your current layout to point to the table occurrence name you actually plan to use AFTER the switch.
4. go to your original layout, select all, and copy the entire layout.
you now have objects on your clipboard, all of which are pointing to what you intend to be the table occurrence name in your NEW layout.
5. go to relationship manager. change the original layout table occurrence name back to whatever it was, then change the temporary name of your NEW table occurrence back to the name you want to use for it. it should MATCH the name you just changed your original layout to, such that all the objects on your clipboard are pointing to the table occurrence name you give your new table.
6. make your new layout, make the default data source your new table, paste in your objects, and you've got a layout pointing where you want.
when i forget, maybe ill find my own post. ha.
Yes, it's the old "switcheroo". You can do similar for copy/pasted scripts, change the table occurrence names to match.
There is an external application for this, Clip Manager. It allows you to see and manipulate (Find/Replace) on the source XML, which is what ends up on the clipboard in binary format if you copy. Clip Managers coerces it back into text, so you can edit it. I haven't used it much, but it has worked well when I have. It is kind of expensive however; but all developer tools for FileMaker are; small market I guess.