From the MSDN Forums:
If you right-click the TableAdapter in the Dataset Designer and click
‘Configure’ the TableAdapter Configuration Wizard opens where you can
reconfigure the main query that defines the schema of your table. This
should leave the additional TableAdapter queries (the additional
methods) that were added after initial configuration.Of course the additional methods will also need to be reconfigured if they reference a column that has been removed from the table on the
database, or if any of the column definitions change (for example, if
the data type is changed or modified). So if an aditional column was
added to the table and it allows Null values the existing methods
should still work – just depends on the scope of change to the schema
of the table in the database.