I don't know anything about Minecraft, but if there's a public API that can check Minecraft names then in theory it's just a case of setting up a custom field that is required during registration which uses a validation callback to check the entered name against the API.
I don't know anything about Minecraft, but if there's a public API that can check Minecraft names then in theory it's just a case of setting up a custom field that is required during registration which uses a validation callback to check the entered name against the API.