assuming the alu hub guard is now glued to the end of the axle and the bearing that needs replacing, i think you can hammer the axle out of the hub from the other side. with the axle out, there're a few things you could consider:
1. dunk the axle/hub guard/bearing combo in a bowl of WD-40 and hope that the WD-40 can seep into between the hub guard and axle, although i'm not optimistic of the outcome. the bearing will get rekt but your aim is to replace it anyway.
2. if you hold the axle with the guard on top (like its an open umbrella), you could rest the hub guard in a vice using it as support, put a bolt into the hold on top of the axle and use gentle persuasion via a big fuck off hammer. since you're hitting onto the axle directly, there shouldn't be sideway impact like you would if you were to try to hit the hub guard off the axle.
to protect the axle threads, i find it best to use a spacer (NOT A WASHER) under the bolt head (i.e. between the bolt head and the axle). this small spacer needs to be of a smaller diameter than the inner of the bearing so that it doesn't stop against the bearing. with the spacer in place, do up the bolt semi tight (make sure the bolt is long enough to no less than 5 threads in the axle. i don't know the actual safe number, but i wouldn't want less than that), then wack it hard while chanting "i will use anti seize between metal parts" over and over