Row Header name change for visual

This one was quite a challenge. Did it dynamically in Power Query : Pair the months and calculate variance for the second month in each pair. You do not need to rename your variances 1, 2 in the source table. Just keep it as in the initial raw data "Variance". Or even better, don't even include the row Variance. I added some tricky magic with empty space based on the number of the index to manage the naming to be always displayed "Variance" 😉 And the last Index column will help you to properly sort your table. Enjoy! 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8krMU9JRMjZRitWJVnJLTQJyTM3AnLDEoszEvORUoIiREVjEN7EIJA1R61hQhNCIpFbXyACquBLIszAHc7xKQbaYmGIoNjGCyueAFEN0OpamAznmBhiKDYFCsQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Period = _t, Report = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Period", type text}, {"Report", Int64.Type}}),

 // Filter out the "Variance" rows
    #"Filtered Rows" = Table.SelectRows(#"Changed Type", each [Period] <> "Variance"),
    
    // Add Index column
    AddIndex = Table.AddIndexColumn(#"Filtered Rows", "Index", 0, 1, Int64.Type),

    // Pair the months and calculate variance for the second month in each pair
    AddPairIndex = Table.AddColumn(AddIndex, "PairIndex", each Number.IntegerDivide([Index], 2)),
    Grouped = Table.Group(AddPairIndex, {"PairIndex"}, {{"AllData", each _, type table [Period = text, Report = Int64.Type, Index = Int64.Type, PairIndex = Int64.Type]}}),
    CalculateVariance = Table.AddColumn(Grouped, "Variance", each let
        pair = [AllData],
        first = pair{0}?,
        second = pair{1}?
    in
        if second <> null then second[Report] - first[Report] else null),
    ExpandedVariance = Table.ExpandTableColumn(CalculateVariance, "AllData", {"Period", "Report", "Index"}),

    // Create a table for variance rows
    VarianceRows = Table.SelectRows(ExpandedVariance, each [Variance] <> null),
    VarianceTable = Table.AddColumn(VarianceRows, "MyPeriod", each Text.Repeat(" ", [Index]) & "Variance"),
    VarianceTableFinal = Table.SelectColumns(VarianceTable, {"MyPeriod", "Variance", "Index", "PairIndex"}),
    #"Renamed Columns" = Table.RenameColumns(VarianceTableFinal,{{"MyPeriod", "Period"}}),
    RenamedVarianceTable = Table.RenameColumns(#"Renamed Columns",{{"Variance", "Report"}}),
    #"Removed Duplicates" = Table.Distinct(RenamedVarianceTable, {"PairIndex"}),
    #"Added to Column" = Table.TransformColumns(#"Removed Duplicates", {{"PairIndex", each _ + 0.1, type number}}),
    // Combine the original and variance tables
    RemoveVarianceColumn = Table.RemoveColumns(ExpandedVariance, {"Variance"}),
    CombinedTables = Table.Combine({RemoveVarianceColumn, #"Added to Column"}),
    SortedCombined = Table.Sort(CombinedTables,{{"PairIndex", Order.Ascending}}),
    #"Changed Type1" = Table.TransformColumnTypes(SortedCombined,{{"PairIndex", type number}}),

    // Final sorting and renaming
    #"Sorted Rows" = Table.Sort(#"Changed Type1",{{"PairIndex", Order.Ascending}}),
    #"Removed Columns" = Table.RemoveColumns(#"Sorted Rows",{"Index", "PairIndex"}),
    #"Changed Type2" = Table.TransformColumnTypes(#"Removed Columns",{{"Report", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type2", "Index", 0, 1, Int64.Type)
in
    #"Added Index"

If it answers your query, please mark my reply as the solution