Yes, I had to remove the calipers and yes, the spring plates are very hard to reseat. What I do is squeeze one pair of oposite pistons with my hands, go between them with one end of the plate, then the other pair. Still, it takes few shots to do it.
As for the copper grease, I had that problem many years ago as I had no idea how much lube to use. Now I know and have no problem at all.
Front brakes - you remove little silver plate from back of the pad, clean everything very well, rest all parts on the rag, not on the ground as when you lube it, it can't have any stones, dust or else. All parts have to be perfectly clean. And yes, clean everything else as well. Push the pistons a bit out and clean them well all arround, then arround them, inside calipers, sliding pins etc... Now, back to pads. After everything is clean, using your finger tip put very, very tiny coat of copper grease on the back of the pad, before putting the silver plate on. The coat has to be so tiny that you can't even see it, just feel it sticky if you touch it. Make sure to grease all the surface, arround the holes too, but not on the sides of the pad. All the area that silver plate is going to rest on has to be coated but nothing else. Now put the silver back plate on. Get the grease again on the tip of your finger and draw the circles where the pistons are going to touch. You will see perfectly marked circles on the silver plate where pistons are touching. This time you can use a bit more grease but not too much. That's it, don't lube anything else. Ah, if you wish you can lube the threads on the screws and thread on the slider pins. Just the threads, not the rest. The lube is going to serve as anti-seize.
Rear Brake - All the procedure is the same as for the front but on the pads is a bit different as they have white pillow between the pad and silver plate. So, after cleaning everything, do not lube between the pad and white pillow, then lube very tiny coat between white pillow and silver plate and then on the top of the silver plate a circle for the piston on outer pad and on inner pad (no piston there) try to draw the area where the metal "jaw" is touching the pad.
It is very important to draw those circles only with the lube because if there was a lube all arround, on first contact between the piston and the pad there is no dry area on the pad for piston to freely push the excess of the lube away and (happened to me once) too thick coat between the pad and silver plate may push the pad against the disk not in perfect 90º angle and you'd feel very weak brakes.
2017 DL1000 White
2014 DL1000 Red (sold)
2012 DL650 White (sold)