insert row with specified values if condition met

You need to add an index column for sorting later and create a table with the Score rows to insert.

Append the score rows to the original table and the sort back into original order.

Finally, remove the Index column.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("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", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column = _t, Custom2 = _t, Custom = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column", type text}, {"Custom2", type text}, {"Custom", type text}}),


    AddIndex = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),

    ScoreRows = Table.SelectRows(AddIndex, each Text.StartsWith([Column], "Question")),
    ScoreRowsExpanded = Table.TransformColumns(ScoreRows, {{"Column", each "Score"}}),
    ScoreRowsFinal = Table.ReplaceValue(ScoreRowsExpanded, each [Custom2], "", Replacer.ReplaceValue, {"Custom2"}),
    ScoreRowsFinal2 = Table.ReplaceValue(ScoreRowsFinal, each [Custom], "1", Replacer.ReplaceValue, {"Custom"}),

    CombinedTable = Table.Combine({AddIndex, ScoreRowsFinal2}),

    SortedTable = Table.Sort(CombinedTable, {{"Index", Order.Ascending}}),

    FinalTable = Table.RemoveColumns(SortedTable,{"Index"})
in
    FinalTable