Bonjour,
coller la macro suivante sur la page code de la Feuille,
Private Sub Worksheet_Change(ByVal Target As Range)
Dim plg As Range, k As Long, isect As Range
Application.DisplayAlerts = False
k = Target.Row
Set plg = Range("G" & k & ":I" & k)
Set isect = Application.Intersect(Target, plg)
If Not isect Is Nothing Then
If Application.CountIf(plg, Target) = 3 Then plg.MergeCells = True
End If
End Sub