Ever viewed the System Tables in Access? Tools>Options>System Objects. You'll now see the additional core tables in Access. BE CAREFUL... back up any database you are working on so you don't muck it up!
AFTER you have a saved specification in the database, there exists the MSysIMEXSpecs and MSysIMEXColumns tables. You'll need to look up your specification ID in the Spec table to look up the columns in the Columns table.
You can make changes to the spec now. Be careful, many of the datatypes are coded, so it takes a little bit of work to figure it all out.
As well - you CAN'T ADD records (ie. add a column) using the table interface. BUT there is a workaround. You can use SQL queries to append additional records.
If you're really good, you could build dynamic specs on the fly with code, and call them using transfertext. Cool Stuff!
It beats rewriting a spec everytime you make a mistake!