Bonjour,
Teste et adapte à ta convenance (cellule cible, F1) :
Sub Test()
Dim I As Integer
With Range("F1")
I = InStr(.Value, Chr(10))
With .Characters(1, I).Font
.Name = "Calibri"
.Size = 11
.Bold = True
.ColorIndex = 3
End With
With .Characters(I, Len(.Value)).Font
.Name = "Arial"
.Size = 15
.Underline = True
.ColorIndex = 5
End With
End With
End Sub