let
    Source = Excel.Workbook(File.Contents("C:\Path\Шапка в несколько строк.xlsm"), false),
    sheet = Source{[Item="xl",Kind="Sheet"]}[Data],
    headRowCount = List.Count(sheet[Column1]) - List.NonNullCount(sheet[Column1]) + 1,
    curColNames = Table.ColumnNames(sheet),
    headTable = Table.FirstN(sheet, headRowCount),
    dataTable = Table.LastN(sheet, Table.RowCount(sheet) - headRowCount),
    newColNames = List.Transform(curColNames, each Text.Combine(List.RemoveNulls(Table.Column(headTable, _)), " ")),
    result = Table.RenameColumns(dataTable, List.Zip({curColNames, newColNames}))

in
    result