Okay, see how it will works for you
==========snip
ElseIf TypeOf ent Is AcadDimDiametric Then
If ent.TextOverride = vbNullString Then
ent.TextOverride = "Dia" & m & "=" & ent.Measurement
Else
If InStr(1, UCase(ent.TextOverride), "%%C", vbTextCompare)Then '//<--should work both for %%c and %%C
ent.TextOverride = "Dia" & m & "=" & Replace(ent.TextOverride, "%%c", vbNullString)
Else
ent.TextOverride = "Dia" & m & "=" & ent.TextOverride
End If
End If
m = m + 1
=========snip
