I need a formula that will open an alternate version of a form to populate a field, save, and then edit a couple of fields on the full form.

Two comments

API _Edit Record will Edit a Record. It does not stop midway for user input.

The syntax for getting a Formula a Rich Text field is more difficult. I suggest that you get a regular formula URL working first.

I suggest that for readability you use formula variables.

You can probably get this to work with using �?a=er to have the user Edit the record manually, and then use NextURL=. ...

So it would be like

var text ManualEdit = .........a=er....;

var text Edit = ......API_EditRecord ....;

var text DisplayRecord= ..... ?a=dr....;

$ManualEdit
& �& NextURL=� & URLEncode($Edit)
& �&URLEncode(�&rdr=� & URLEncode($DisplayRecord))