Just like in the real world, you don;t need a deed poll, you can call yourself what you like as long as it is not for criminal purposes, or in the case of AB, if it not to become a troll.
You might be able to get a close relative to register a new name and let you borrow it occasionally. I have had to do this in emergency situations, and then when you are unfairly challenged, you can state truthfully, that was my brother not me.
You also have to be aware that you are absolutely not allowed to have another name that is the same or even remotely similar to another user. If you do it means you're a troll, (it's in the small print).