Just some notes on this subject. I've done two of these and it ain't easy.
1. It is very hard to "cut the old Metz off". Not only does the Triumph wheel have no center drop to it it has a very short lip and it is almost impossible to get any kind of cutting device in there. The bead of the Metz contains a large steel cord that must be cut to do this.
2. If you put large amounts of lube on the bead of the tire when mounting it, the tire may very well spin on the rim during hard acceleration or braking, causing all sorts of problems. This may feel like your clutch is slipping (Hey Piggr!), it may feel like your brakes don't work, and it will throw your wheel out of balance.
3. If you use an automotive style machine there is nowhere to clamp onto the rim without marking it up. There are adapters made specifically for motorcycle wheels but they like to slip.
4. I used small blocks of wood to hold the bead away from the lip on the last one I did (to simulate the missing drop center) and this helped a lot.
5. I've never seen anyone "lever" one of these off or on but that just has to suck. It would have to take lots of large levers and lots of large help.
6. Part of the problem is the Metz itself, if you let the air out and break the bead it turns into a uncontrollable flimsy walled pile of crap with an indestructible bead. Its much harder to work with than a car tire.
It sounds like this isn't the first Rodeo for S.B.'s mechanic. I've put marks in both rims I've done (Rusty's and mine) but I think I'm to the point where there won't be any future marking of rims.
You would think that Triumph would focus on this in their training courses. Maybe they do and it just isn't getting done right. They put them on at the factory without screwing the wheels up, so it must be possible.