LK is the Boeing customer code. This code will be different per customer.
Sure. The general ID would be 767-200, complemented by a C to make it 767-200C, because it is considered a convertible version. So, 767-2LKC makes it a 767-200C for customer "LK", which happens to be the USAF for the KC-46A, which is a USAF designation (nothing to do with Boeing...)
Just found the KC-46A is NOT a 767-200, it's NOT a 767-300 and it's NOT a 767-400. It's a 767-200 fuselage with 767-300 wings and 767-400 stabilizers.... So it might be a 767-2C after all. Let's hope for some more info next year