I have an ibanez RGR321 EXBK with INF1 and INF2 pickups and my amp is a bugera 6260 head + 4x12 cab, i mainly play metal and the inf pickups kind of lack punch and compared to emg's, the inf pickups are way worse for metal, so my question is
Is it worth changing the pickups to like dimarzio D-activators or any similar passive pickup good for metal, would it be a big difference when playing metal?
And one kind of noob question, is it possible to just change 1 pickup, like changing the bridge pickup to a D activator and keeping the inf pickup for neck.
Guitar: Ibanez RGR321 EXBK

Amp: Bugera 6260 head + 4x12 cab
Seems like you have a pretty good amp and set up already, certainly your wood may well be quality enough to warrant some better pickups, just remember to look outside the box, are you settled on Di Marzio? or would it be worth looking at how much another guitar with duncans or EMGs might cost? It's up to you and you'd be saving money and it may well make your guitar nicer, we've all probably seen the dude on youtube with the hello kitty strat with his EMG 81 in the bridge, but I've upgraded pickups before and found it only hurt me in the long run.
Washburn X-40 Pro
Washburn X-40
Yamaha RGX 320s custom (with Duncans)
Ibanez GRG 170DX
Yamaha Pacfica 120V (lol)
Encore Strat pile of **** (mega lol)
Saving for new amp
with you rig right now it would make a decent difference. You could change just one pickup if you wanted to, but then you'll have one good pup and one cruddy pup.

my recommendation is:
Bridge pup - Dimarzio Drop Sonic
neck pup - Dimarzio Humbucker from Hell
My Gear
-Gibson Les Paul Studio
-Ibanez "lawsuit" Les Paul
-Ibanez S470
-PRS SE Custom

Marshall TSL100
Marshall 1960a cab

Dunlop 535q wah
Visual Sound Liquid Chorus

i have a rg320dx (1998) withan emg hz h3 in the neck and a s.d. screamin demon in the trem position. YES it is worth it to change. i started with just the neck pup change. the difference made my stok trem pup sound like poop. so i then changed the trem pup. yes just change the one you are most unhappy with first. most pup websites have sound demos to give you an idea of the sound they produce.