1. Yes, you can remove the outer burr, it's a bit more of a hassle and you will need a small torx bit
2. For the love of god, don't mix and match burrs like baldheadracing suggested. If they were not design to go together, they won't match. You will get bad grind results at best (too much gap) or destructive burr contact at worst.
3. There is no room left in the wall to remachine the grinder to take a 48mm burr. I've worked extremely hard to make this grinder as small of a diameter as possible with a burr as big as possible, The wall thickness of the body and mechanism is less than 0.5mm in places with internal features.

Peter, do you have any recommendation to fix the rubber sleeve from slipping?

Yes, take it off.
I don't use it and I mostly manually grind. I don't have any problems with the grinder slipping in my hands without the rubber sleeve, even tho I have relatively small hands.
We added the rubber sleeve for people that might really have big problems with the grinder slipping (mostly girls with extra small hands and less gripping strength). We could have indexed it with detents in the body and sleeve, but then the grinder would look ugly with the sleeve removed, and I was very against that.
At first the idea was to ship the sleeve next to the grinder, but then it was decided that it will be shipped on the grinder. And now everybody seems to want to keep it on for some reason.
Well I don't; I never put it on my personal grinder in the first place.
I consider the sleeve a free ad-on, not an integral part of the original design.

One could also use rubber cement to attach it, if one really wants to keep it on and is not happy about it staying perfectly aligned all the time, I guess...

It seems that mine started to exhibit a first symptom of "wear"... the outer metal part of coffee canister enlarged, and the first attempt in this morning to remove from the body by rotating, after grinding, led to a big surprise... nothing happened
Pulled vertically and it finally disengaged, showing the magnets ring out of place some 3-4 mm. And rotating quite loosely...
I don't want to glue definitively, so will try to use some plastic alimentary foil to increase the friction where it was from the factory.

I've been really enjoying the Arco, but is anyone else having an issue with beans getting stuck on the bit that sticks out by the top of the burrs in the grind chamber? Feels like every time I grind there's consistently one or two beans sat there unless I tap the side of the grinder which I don't really like doing. I think they should have machined this section so it has a much steeper angle so nothing can get stuck. Other than that I've been really enjoying using the Arco so far, just slightly frustrating in use at times

Happened for me too, especially with heavily RDT beans.
No RDT and a single lateral twitch, of the whole machine, when I hear the grinding ended, and no more beans stuck.
Nothing is perfect...

Can a blower be used to reduce retention (instead of slapping or tapping the grinder)?

You mean probably for espresso, because for brew I want that retention, it means chaff and fines, nothing that I want in my filter.

If a spare part like the attached, planetary joint bellows, having 32mm the smaller diameter can be found, you can try.
32mm is the diameter of the beans feeder entry hole.
Or, simply blow with the mouth for a quick test.

renatoa wrote:You mean probably for espresso, because for brew I want that retention, it means chaff and fines, nothing that I want in my filter.

If a spare part like the attached, planetary joint bellows, having 32mm the smaller diameter can be found, you can try.
32mm is the diameter of the beans feeder entry hole.
Or, simply blow with the mouth for a quick test.

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So the problem is more beans getting stuck in the hopper, so not really the fines etc. I'll find that I grind but the output is say 0.5g less than what I put in, I'll then take the hand grinder portion off only to see one or two beans still in there sat around that edge above the burrs. I do use RDT for the static, however it's only one spray, and I have tried with no RDT and beans can still get stuck.

It's not the end of the world, and certainly not a reason not to buy the grinder (as others have said, nothing will be perfect), it's just annoying that either not having the edge, or having a longer taper on the edge would mean this wouldn't be an issue, RDT or not.

Might give some bellows a try though, has to be better than knocking the grinder

Its a bit of a side-to-side shake, rattle & roll to get the last bean or 3 to drop down into the burrs apart of electric grinding with my Arco. Then, to get the retained grounds off the bottom side of the grinder, I remove the grinder and give it a couple gentle knocks onto the wood cutting board it sits atop. That is the only method I have been successful with to get the ~.5g or so of retained grounds to drop down into the dosing cup. I'm wondering if the chute, which feels like plastic to me, under the bottom burr induces more static than it might otherwise if it was metal?

Regardless, as other's have stated nothing's perfect, but it seems to deliver the "goods" to the cup; all the more surprising to me given its relatively low cost and small burr diameter.