Append Table - empty fields default value

When appending a table, at the moment any fields that will be creates will have no value because they don’t exist in both tables.
It would be useful to have an option to be able to define a default value, ideally by column, to be added in this case.
This would typically be 0 for numbers, but could equally be a “marker” to filter/create a new data set for investigation - I know you could filter by empty fields if you only append one table, but if you’re appending many it would be useful to have different “markers” for the different data sets.
I know there are ways around this in EasyMorph, but being able to do this at the point that the tables are appended would speed up processes where you are appending tables which have some different columns.
I’m happy to put together some mock-ups of what this might look like if you think it’s something you would be interested in adding. I’m thinking a similar interface to the top of the Aggregate action for example where you can add the column and then a free form text box so you can specify what you want.