Replace specific value with column name in variable number of columns

Yes, 2nd statement is the answer where Source will be replaced with #"Changed Type". So the code becomes below

let
    Source = Excel.CurrentWorkbook(){[Name="TablePlannedVacations"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Aparupa", type text}, {"Eunice", type text}, {"Floris", type text}, {"Frank", type text}, {"Gijsbert", type text}, {"Jasper", type text}, {"Ken", type text}, {"Mahesh", type text}, {"Mark", type text}, {"Niels", type text}, {"Remco", type text}, {"Rob", type text}, {"Sepideh", type text}, {"Stan", type text}, {"Thijs", type text}}),
Custom1 = Table.FromRecords(
    Table.TransformRows(#"Changed Type", (r) => List.Accumulate(Table.ColumnNames(#"Changed Type"), r, (s,c)=> 
        Record.TransformFields(s,{{c, each if _ = "V" then c else null}})))
        , Value.Type(#"Changed Type"))
in
    Custom1

Hi,

Unpivot, Replace Value, Pivot

let
Source = Your_Source,
Unpivot = Table.UnpivotOtherColumns(Source, {"Date"}, "Attribute", "Value"),
Replace_Value = Table.ReplaceValue(Unpivot,"V",each [Attribute],Replacer.ReplaceText,{"Value"}),
Pivot = Table.Pivot(Replace_Value, List.Distinct(Replace_Value[Attribute]), "Attribute", "Value")
in
Pivot

Stéphane