Progressive Date Columns

Try something like this. I included examples of:

• transforming static and dynamic columns' types
• transforming all dynamic columns
• transofrming specific dynamic colums (using durable 0-index rather than name)

let

    Source = Excel.Workbook(File.Contents("C:\******\******\******\Book1.xlsx"), null, true),
    Sheet1_Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
    PromoteHeaders = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars=true]),

    // specify columns that do not change from refresh to refresh
    StableCols_Names = {"Material", "DOH"},
    // and manually specify static columns' types
    StableCols_Types = {type text, type number},
    
    // grab dynamic column names
    DynCols_Names = List.Buffer( List.RemoveMatchingItems( 
        Table.ColumnNames(PromoteHeaders), 
        StableCols_Names 
    ) ),
    // assuming these are all numbers - may need to update if different logic applies
    // if needed, can implement a prefix on column names that you then use to set the type
    DynCols_Types = List.Generate(
        ()=>0, each _< List.Count(DynCols_Names) ,
        each _+1, each type number
    ),
    // transform column type using static and dynamic names/types
    DynFixTypes = Table.TransformColumnTypes(
        PromoteHeaders, 
        List.Zip( { 
            StableCols_Names & DynCols_Names,
            StableCols_Types & DynCols_Types
        } ) 
    ),
    // example: multiply all dynamic columns by 2 and switch out nulls for 0
    DynUpdateAllDays = [
        target_transform = { each ( _ * 2) ?? 0, type number },
        transform_list = List.Transform( DynCols_Names, each {_} & target_transform ),
        invoke_transform = Table.TransformColumns( DynFixTypes, transform_list )
    ] [invoke_transform],
    // example: divide the specified columns {0..6} by 100 and convert to %
    DynUpdateSpecificDays = [
        target_cols_i = {0,6}, // first and last days
        target_cols = List.Transform( target_cols_i, each DynCols_Names{_} ),
        target_transform = { each Percentage.From( _ / 100 ), Percentage.Type },
        transform_list = List.Transform( target_cols, each {_} & target_transform ),
        invoke_transform = Table.TransformColumns( DynFixTypes, transform_list )
    ] [invoke_transform]
in
    DynUpdateSpecificDays