The rules actually make perfect sense if you take the trouble to understand them.
For the record: I do understand them, but most people do not. I interpreted the OP question as "can you put an adaptor on your charger and get more power from the outlet"? That's dealing with a mixture of electrical theory and regulations, but the practical answer is: no adaptor, plug or outlet is going to change the behaviour of the charger or the car.
You can have multiple circuits with 10A outlets and they may well draw up to 20A , but the loads would be on different power points.
You can indeed have multiple outlets on a breaker. The past owners who built and rebuilt my house thoughtfully installed an amazing number of outlets in truly convenient locations. The result is that a builder with a suspect saw can plug into an outside GPO and take out the kitchen, my office, and a bathroom which are in diametric corners of the house and on different levels. Very unhelpful mapping of outlets to breakers. In the last two months my electrician has finally understood that I don't run a typical house, and 4 breakers for the entire house can't cope. FWIW, our 10A outlets are now spread across 15 breakers on three boards (plus three three-phase outlets, plus six 15A outlets, plus an actual 20A GPO) and it's not quite finished. Possibly excessive, but becoming more balanced.
Mitsubishi initially supplied the charger with a 15A plug to make people use a dedicated circuit even though the charger was only pulling 10A max.
If that's the case, it's spectacularly specious logic in the part of Mitsu.
And I think you misunderstood my comment about it's trivial to change the power point (which it is). That should not be done by anyone other than a licensed sparky, who will also know the rules and who should do what it takes for that outlet to be compliant. Quite probably that would mean a dedicated breaker.
They figured if people charged their car on a 10A circuit and then other loads were plugged in on different points such as a fan heater, it would trip the breaker. Having said that, you can buy an adapter that allows a 15A plug on a 10A power point, most caravan shops and mayb bunnings sell them. They have a 10A breaker in them, so they are legal. Later mitsu supplied a charger with a 10A plug but it woul only draw 8A.
Sure. And that's one of my greatest annoyances with the Outlander PHEV. Given that it can absorb power at speed via the ChaDeMo connection, why did they limit the Type2 connector to single phase? Why not have it work with a single phase via the granny charger, but actually take lots of power if that's available (as it now is here... we have three phase outlets and a Fronius WattPilot).
Anyway, getting very OT. Maybe.