rename columns

Hello - it would be best to do this in Power Query.  You can do this by adding a new step to each table and use the Table.TransformColumnNames function, like this:

RenameColumns = Table.TransformColumnNames ( Source, each Text.AfterDelimiter ( _, "." ) )

Here is the full sample table with script:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSAeJYnWglIyDLCMwyBrKMlWJjAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [source_dim.Test1 = _t, source_dim.test2 = _t]),
    RenameColumns = Table.TransformColumnNames ( Source, each Text.AfterDelimiter ( _, "." ) )
in
    RenameColumns

BEFORE

AFTER