Once you get those screws out don't worry about putting them back.
They are used for ease of assembly during manufacturing and are not required.
I threw them out a long time ago and I have no issues with vibrations or uneven wear even through I change my tires at least 2 times a week because of all my racing.
Yup, use penetrating oil and a hammer driven hand impact tool (might can rent / borrow / buy (to use again) from your local parts store. Use the right phillips tip in the set! If it's stripped the head already, then drill out is next step. Screw doesn't really serve any use after the wheel is back on anyway.
I always hated those little bugges myself, back in the auto tech days :evil: Fussing around with those sometimes doubled the amount of time it took to do a brake job which always included 'turning' the rotors.