Yes, you can add a new field to a table using SQL.
CREATE TABLE t (mfd_id INT64, INDEX mfd_id_x BTREE (mfd_id));
ALTER TABLE t (ADD f INT32);
The first statement creates a table, the second adds a new field.
You can use this with tables stored in a MAP file or with tables stored on a different data source. In the latter case, if you are running the query using 9's query engine, 9 will translate the syntax for that other data source as necessary.
We do not currently add fields during copy / paste. We might allow doing this in the future.