This example inserts "for your personal use" if the Company merge field is blank and "for your business" if the Company merge field is not blank.
ActiveDocument.MailMerge.Fields.AddIf Range:=Selection.Range, _
MergeField:="Company", Comparison:=wdMergeIfIsBlank, _
TrueText:="for your personal use", _
FalseText:="for your business"