Exactly. The conditions aren't the same now as prior to the illegal Merc test. What they're suggesting would be akin to all the teams deciding to run hand operated suspension adjustment the race after they were banned on the Red Bull car.
I agree, but even that comparison is unfair on Mercedes, because there is no arguable interpretation of the rules according to which Red Bull's ride-height adjustor mechanism was legal. If it was capable of being adjusted by hand, which it was by Horner's own admission, then it was illegal whether they used it or not. So the scrutineers didn't ban it, it was already banned, they just asked Red Bull to take it off the car. And they failed to refer to the stewards the fact that Red Bull had competed in races with the illegal mechanism.
Mercedes were investigated by the FIA and the IT and found to have broken the rules although they acted in good faith. Red Bull were not investigated by anyone even though they definitely broke the rules, and we know that because Christian Horner went on the record and admitted as much. If somebody were to run a test mirroring the Pirelli/Mercedes Barcelona test, they would quite rightly have the book thrown at them because the thing has been investigated before and found illegal, so the stewards or tribunal would be forced to conclude that anybody doing it now, in the light of that ruling, had cheated on purpose. That includes Pirelli, who have already been reprimanded for this. But if somebody turns up to scrutineering at Silverstone with a ride-height adjustor mechanism exactly the same as what Red Bull had last year when they were told to take it off their car, it's hard to see how the scrutineers could do anything other than tell them to take it off their car. I expect they check for it in the pre-event checks these days, though, so there would be no point doing so as you'd have to change it before the race anyway.