Sinon reste le remplacement
Sub Remplacer_Mois()
With Columns("A:A")
.Replace What:="jan", Replacement:="janv", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="feb", Replacement:="févr", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="mar", Replacement:="mars", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="apr", Replacement:="avr", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="may", Replacement:="mai", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="jun", Replacement:="juin", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="jul", Replacement:="jui", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="aug", Replacement:="août", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="sep", Replacement:="sept", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="oct", Replacement:="oct", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="nov", Replacement:="nov", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.Replace What:="dec", Replacement:="déc", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False
.NumberFormat = "yyyymmdd"
End With
End Sub