I would personally find it a bit rude to ask them to switch. 1K is a preferred seat and presumably if the person who pre-assigned it had preferred something else he/she should have chosen it? I personally would not like to be asked: I prefer row 1 (especially on the A380 and 777, personally even on the 744 although I understand why some people do not) and at the same hard it is hard to say no when someone asks you if they can sit next to their travel partner especially (if I can count 21+3 correctly) on Christmas eve!

I think it is great for you to call and select 1A if you want, but I personally think that trying to politely drive the person entitled to pre-assign it out of it is stretching a bit.