You can freeze or lock fields with their current results so that they won't
change even if the data is changed or disconnected. With the form
unprotected, right-click on the fields involved and lock them individually.
(This can be done with a macro but I'm doubt you are up to writing it. You
could get help in the vba beginners group. You would want to lock only
mergefields or only formfields.)

To get merge results into a document with active formfields, you set up the
merge and preview the results on screen using the <ABC> button on the merge
toolbar. At this point, you haven't "performed the merge" but you have a
document that looks like you have. At that point you could lock the merge
fields and save your result document. Then, independent of mailmerge, you
protect it for forms and fill in your formfields. This is the method I use,
but I am only preparing documents based on a single record.

If, on the other hand, you are doing merges of multiple records but the
information in the formfields will be the same for all of the records, you
could lock your primary merge document for forms, fill in the form fields,
unlock the form and lock the formfields and then actually run a merge for
the multiple records. I suspect that using ASK or fill-in fields would be
more productive, though, especially if your formfield info changes for
different records.

Probably clear as mud. Sorry, but I've got to get back to my paying work.