In my case (and in the case of some other customers of other MVNOs), my carrier, Straight Talk, is really just a company that buys wholesale access to AT&T's network and then resells it as a prepaid service to customers. Thus a Straight Talk SIM card looks identical to an AT&T SIM card to the iPhone. And AT&T's iOS carrier profile blocks access to the APN editing submenu. So my situation is different from yours because in your case, your Brazilian service provider and your European service providers had no corporate connections with each other, nor did they share a singular common network, as is the case with AT&T and Straight Talk.
There is next-to-nothing Straight Talk can do about this, at least without both AT&T's and Apple's co-operation.