Sure thing Patrick. Do note that when I first did this it was out of wondering what the bearing looked like inside before I ventured the idea of replacing the bearing. I had some new bearings on hand and know how to do it, but I had to know if it really needed replaced, or was just shy of grease. So yes, pop the seal carefully, I used a robust razor blade from a box cutter. On the first one I did, from a Specialized hub(1980s !), the grease inside was like thick peanut butter and sparse. I knew that one needed a flushing to break it up. I used some WD-40 the first time, but it's not the most robust grease-breaker-upper. So oh ! I have a can of brake cleaner on hand, much more to the point, and just a squirt, run my finger around it(with nitrile gloves on !), bearing side up/vertical. Then I sprayed some low pressure compressed air in there to expel it as best I could, this time with wheel vertical with a rag covering the spray as to not spray me. Do wear safety glasses. Good enough. Now lube. I chose to use Lucas White Lithium grease in the 8 oz. tubes(don't use crappy spray WL grease, it's not the same). Real WL grease from the can or tube is much like if not the same as ye ol' Campy grease. It's not as heavy as say marine or even Phil/Park grease, but it has it's own unique lube character though, one that I cannot describe in words. It seems to be more "slippery" in use. I use it in VP pedals also, and when I take the bodies off the axle, the grease almost looks "wet" and is very slippery, but with body to it. It's funny that the Lucas package says "not for wheel bearings", that's auto wheel bearings it refers to, not bicycle wheel bearings. Totally different applications !
All that aside, I squirt the grease inside and again use my finger to work it and around. When I placed the seal back on any excess was pushed out the sides, and in initial use there was a tiny bit more to wipe off. Then none.
The cleaning is not necessarily needed if the grease inside is just sparse but relatively functioning, and adding more of the same. If using another grease like WL then I'd clean it out beforehand. I also have some Suntour XC Pro Greaseguard hubs that have some white grease in it from the factory, I assume it's WL as I don't know of any other white grease. While those bearings can be cleaned like regular cartridges, it's not needed as the new grease pushes out the old through the outer seals. It's no different that cars and farm tractors with zerk grease fittings. The grease inside never needs removed, just replenished with more, pushing out the old. The main thing is to have lubricant in there.
Fuuny thing though, I once thought one of my wheels with a Phil FW hub had a bad bearing. I had the tire off, in the wheel stand, listening carefully. Surely it seems the bearing was making a tinny cracking noise. I hesitated though and set the wheel aside. I had another to use. After so many months, one day spinning it slowly, I realized the sound was not from the bearing, but the rim, a Mavic A719. Sure enough, there was tiny bit of aluminum that had come off inside the rim. I finally got it out, and sure enough, no more noise. Had I replaced the bearing right away I would have done so needlessly and in futility !