If you cancel your registration is before the deadline (which is about a week before the competition), then you are normally refunded 75% of your registration fee (50% is normal for the UK Championship.) Each competition will set out the cut-off date for the partial refund and you can find that on the competition webpage on the World Cube Association (WCA) website^1.

The system behind the WCA website does not enable the UKCA² team to be able to transfer registration from one competition to another. The UKCA volunteers are unable to change this. The UKCA is not-for-profit and run by volunteers. All monies paid for competitions go towards venue and other costs including a payment to the WCA for the use of their website and registration software.

Glossary:
¹ The governing body for Speedcubing.
² UK Cube Association, the UK’s recognised regional organisation for organising Speedcubing competitions to WCA standards.