When you put the cover lid lid on the lid hits the top of the plug and you compress the top ring, right? Simply can't move up and out of engagement on it or the smaller ID/OD ring either.
Thermally, it wouldn't care about expansion as aluminum expands with the temp change and the plug does the same thing at the exact same rate.
Neither can move more than the big "O" rings could accommodate easily.
Silicone "O" rings are the most heat aging resistant kind, and are more oil degradation resistant than Bunta N rings which are used elsewhere in the bike.
Lots of other things in the engine would give up before this sort of plug system would .....
As far as trying them out, simply start supplying them and keep track over the years. Time to first failure will likely be greater than a cam chain life, so you really aren't going to get a simple short test result in any case.
Your issues will be operator error (nicked rings, etc) and rough casting machining type edges and such like stuff.
Plus folks trying to use this trick with silicone sealant on top of it.
("O" rings only work when put in with a light grease film to ease their insertion, but otherwise it is a dry installation for an "O" ring seal).
Lack of a good Instruction Sheet is your main potential failure mode, in other words.
Is this your excuse to buy that little CNC lathe you've been thinking about?
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