Ummmm.....I'm thinking if the ECM has detected an evap emissions fault, it'* possibly electrical in nature. Checking the purge valve might not be a bad idea (the solonoid on the top of the evap canister). It should have some value of fairly low resistance.....not open, not shorted. You can also jumper one pin to ground, and the other to 12v. You should be able to hear and feel the solonoid engaging and disengaging. There'* a small port on the solonoid body. Connect a piece of clean tubing to it. With the valve open, you should be able to blow through it, closed, you won't If you can in either state, the valve is stuck open, if you can't in either state, the valve is faulty and won't open.
As far as changing the filter, I don't know how to open the canister.....and it'* buried under my airbox. My airbox will be out tomorrow, so I can check it then if you don't have an answer yet.