"What I want to know is why (actual facts) the ECU should not be allowed to be modified outside the box with what can already be done now legally inside the box (just more expensively)."

I think you answered your own question. The original intent was to allow after-market chips, re-programming, etc. - I cannot fathom why the words "or replace" were included because that has opened up a whole new can of worms. Like someone pointed out, if you take the next step of rules creep and allow the harness connectors to be changed, you might as well say that engine management is unrestricted. Everyone will have to have one to be competitive. I firmly believe that it is not too late to roll back the rule and delete "or replace" from it, and that we should do it. It is not too difficult to open the box and check if the OEM ECU is in there, even if highly modified.