It's MUCH easier to do the reverse: Enter data into separate fields and then use a calculation to combine them.
What makes this a messy situation to split them is that names don't all fit the same pattern. A first or a last name might actually be two words instead of one.
Let ( NameList = Substitute ( FullNameFieldHere ; " " ; ¶ ) ;
GetValue ( NameList ; 1 )
Let ( [ NameList = Substitute ( FullNameFieldHere ; " " ; ¶ ) ;
LastName = RightValues ( NameList ; ValueCount ( NameList ) - 1 )
Left ( LastName ; Length ( LastName ) - 1 ) //strips off extra return character put at end of text by RightValues function
that did it - I just have to edit a few instead of 4000.