Are juicy five calipers identical front and rear? i.e can I put a front caliper on the rear?

Dunno offhand, but normally a front caliper with IS mounts will fit the rear but for the next disk size down
eg 185 on the front becomes a 165 on the rear – obviously you'd need the appropriate disk too

Yes they can. I recently bought 2 "rear" juicy 3s and fitted one to the front. Had to shorten the hose, and the olive was a long way "outboard" but it worked fine

Yes Juicy 7s 2x rear on my Five

groovey cheers! i'm gonna have to have to change the cable, so will have to lookat all the instructions… but what is an olive? Do i need a different one to make a front caliper an rear caliper?

the olive is the little metal sleeve that compresses onto the hose when you tighten the fitting into the caliper. When you buy the bleed kit that you'll need there'll be instructions and all the bits you need included.