Couldn't wait, found a workaround that works for me...
Code:
With ActiveCell
fst = InStr(8, ActiveCell, ":")
'Format INV BOLD
.Characters(fst + 3, ActiveCell.Characters.Count - 4).Font.Bold = True
.Characters(fst + 7, ActiveCell.Characters.Count).Font.Bold = False
'Format INV number size
.Characters(fst + 3, ActiveCell.Characters.Count - 4).Font.Size = 20
.Characters(fst + 7, ActiveCell.Characters.Count).Font.Size = 11