Bonjour,
Essaie ainsi :
let
Source = Excel.CurrentWorkbook(){[Name="Tableau1"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"COMPTE", type text}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each if Number.From(Text.Range([COMPTE],4,1))=1 then Text.Range([COMPTE],0,4) & "99" else [COMPTE])
in
#"Added Custom"
Attention ! tableaux base 0
Cdlt.