Besides a manual transmission, what kind of "mods" are you interested in? Cosmetic? Audio? Handling? Braking? Acceleration? If the car's been sitting for 10 years, does your mom really NEED to be able to drive the car? Although there's a lot involved in switching a car from an automatic to a manual so I do not recommend that. You'd probably be dollars ahead to just buy a used Grand Am that started life as a manual.
-Rod