Auto and Manual Categories

Einomi this is standard self-referencing query stuff. But you must have some unique reference for every line of your statement (or date column will be enough if you load transactions for the whole day). I added index column but just for demo. In short: you have some table with "old" transactions in Excel (with auto and/or manual entries) - load it to PQ, load your source data, this way or another filter new transactions only (this is job for your unique identifier), apply your transformations (including auto category and subcategory stuff), combine old and new transactions and load resulting table back to Excel. Now you may manually edit that table and won't loose this info unless you manually delete rows from your table. 

let
    auto = Function.Invoke(
        Record.FromList,
        List.Reverse(
            Table.ToColumns(
                Table.CombineColumnsToRecord(
                    Excel.CurrentWorkbook(){[Name="auto"]}[Content], 
                    "rec", 
                    {"Category", "Subcategory"}
                )
            )
        )
    ),
    loaded_transactions = Table.Buffer(Excel.CurrentWorkbook(){[Name="loaded"]}[Content]),
    loaded_ref = Record.FromList(List.Repeat({false}, Table.RowCount(loaded_transactions)), List.Transform(loaded_transactions[ref], Text.From)),
    new_transactions = Table.AddColumn(
        Table.SelectRows(statement, (x) => Record.FieldOrDefault(loaded_ref, x[ref], true)),
        "cat", 
        (x) => Record.FieldOrDefault(auto, x[Counter Party], [])
    ), 
    xpand = Table.ExpandRecordColumn(new_transactions, "cat", {"Category", "Subcategory"}, null), 
    z = loaded_transactions & xpand
in
    z