wat mods can i safely get away with while my car is under factory warranty was looking at headers and an 3" exhaust with a supercharger down the track

you wont 'get away' with any mods at all.

Mods are "ok" but if something breaks and the can atribute the failure to the mod you've made they will wipe you. I.e if something in your drive line was to fail after you did the headers/exhaust they may not honour the warranty due to the increase in power no matter how small it may be. But with ford it just depends how the workshop manager is feeling at the time.

so ive got 3 years 2 save up for a supercharger then

your best bet is to go and speak with the place you bought it from and have them write down on paper what mods they will allow under warranty and get them to date and sighn it.
that way if you have any trouble later down the track you can throw that bit of paper back in their face.

there was a bloke on here ages ago who had extractors put on a ba xr8 i think it was and few months later he blew his engine and ford wouldnt cough up for it.