[Replicant]

To modify search strings on a per user basis based on their preferences that are stored preferably in a table, there will need to be

A form with the current categories or forums dynamically built to accommodate future categories/forums that will upload the users prefs to the server.
A frontend controller to receive the data and call the insert api to store it in the table.
There would need to be a modification of the template code to query that table based on current userid and set the search query to the users prefs.
There would need to be a product created with the api to do the data inserts and template queries.

This is what I can see would be the least I can think of to get this to work.
It actually seems like it would be a useful mod, I wish I had more time to look at it.