When you block someone on the chat can that person see your new name and alliance from chat history?

They can see you until there chat cache is full. If the cache holds 1000 messages your chat will stay until he gets 1000 messages. sorry but I dont know the exact number. It could be 2 or 5k but eventually your message will be pushed out and he won't see your name change. You can speed this up by asking your alliance to send him random messages