How would that work though? The more success tesla has, the more expensive it would be for elon to acquire the required control. In this hypothetical scenario, he'd benefit more from lowering Tesla's valuation initially in order to make buying the required shares cheaper.
So, my entire post was about the lack of a "threat" or "blackmail" from Elon, despite the way the media keeps presenting it. With regard to your question -- Elon made an off-hand mention of one way to increase his percent ownership, if needed, in the far future. I noted that, and provided a brief explanation. That is all.
But, you are asking how it "would" work -- effectively asking for some certainty in prediction. Obviously, nobody can do that for a hypothetical, far-future event. Of course there are many reasons it might not work, but there are also many hypotheticals that *could* make it work.
Think of it as an exercise in imagination:
Can you imagine a future scenario in which Tesla could be successful enough to have lots of cash on hand, but the stock price could be irrationally low?
That seems like an easy one...so let's keep imagining! Maybe in that same future, Elon feels like his then-current percent ownership is not quite where he wants it to be to control and guide the careful development/deployment of risky technology.
Now, if we put those two hypothetical imaginings together -- can you imagine that maybe, just maybe, Tesla could buy-back enough of those depressed shares to effectively increase Elon's ownership percentage, and nudge his voting control up to where he will feel more comfortable?
You seem to like the idea of Elon "lowering Tesla's valuation initially", so that is one hypothetical...but I think we've all seen over the years many different reasons (or lack thereof) for irrational drops and sustained depression of Tesla's valuation. Combine any of those with lots of cash-on-hand, and the company can effectively buy back shares to increase everybody (including Elon's) percent ownership. If, in this future, Elon is already close-ish to his desired threshold, it seems reasonable to imagine Tesla could decide to do this to get over that hurdle.