What year is the car?
With warranties being popped (i.e. voided) left and right for simple modifications, over-revving, funny tire wear (and on and on), you're almost better off having the dealer (or a reputable shop) change your oil. When I bought my WRX the service manager flat out TOLD me to have someone else (besides myself) change the oil, and that I should keep EVERY reciept and a list of odometer readings corresponding to the oil changes. The warranty game is getting funkier every day...
I do everything myself on my Z (ask my knuckles... they are tired of the abuse!) and no way will I let any shop work on it (except, perhaps, for the roll cage)... But on the WRX... meh... the dealer can handle it.