[Power Query] Split rows into columns, but with some conditions

Hi knyklu 

One way:

let
    Source = Excel.CurrentWorkbook(){[Name="Table"]}[Content],
    NullREP = Table.ReplaceValue(Source, each [REP], null,
        (x,y,z) as list => {null} & Text.Split(y, ";"),
        {"REP"}
    ),
    ExpandedRep = Table.ExpandListColumn(NullREP, "REP"),
    UpdatedEtap = Table.ReplaceValue(ExpandedRep, each [Etap], each [REP],
        (x,y,z) as nullable text => if z is null then y else null,
        {"Etap"}
    )
in
    UpdatedEtap