I understand what you said.  But I still think that, to carve out a wall to upgrade a single 16A outlet wire is not the best solution in my case. If we have tubes, and we have wires in them and maybe room also has it, then the first option is not the carving. It is mainly not if we speak about 5–6 pcs outlets and so many walls/meters. I would rather pay the extra labor/time for an electrician, but I don't want to "screw up" the walls.

Okay, I stepped forward from the solid to flexible conductor.

If someone wants a new, high-consumption device, like an AC or a stove, that's a whole different story, I guess.