Be careful. The fare rules quoted by OP contain the standard UA provision which essentially makes the entire new ticket non-refundable. In addition a penalty will apply. While OP has not listed the full fare rules, that penalty would typically be $400-600 from the UK.
This question gets asked all the time. The answer is pretty much the same. You cannot turn non-refundable funds into refundable funds by upfaring and cancelling.
THE MOST RESTRICTIVE CANCELLATION PENALTY
RULE APPLIES TO THE ENTIRE PRICING UNIT