What sort of syntax would do this?
I think it would be the “correct sort” of syntax – if there was a script set that changes the enter behaviour of fields; but there is none.
What you could do is e.g. set a flag in the record and use it
• for a Hide condition to swap the fields against their merge field counterparts
• with a script trigger that on field enter immediately exists the field, if that flag is set (and maybe the active field belongs to a predefined list of specific fields)
Finally, use the search facility of this forum to see other methods suggested.