We have supported races allowing runners to self-manage their event-event transfers for a while now. This is really useful for someone who entered the Marathon but needs to drop down to the 10K due to injury.
We allow you to set a fee to do this. We also automatically calculate if there is a price difference. If there is an increase in price, we will calculate that and charge the customer. If there is a drop in price, then we do the transfer for free (unless you set a fee).
With the large number of Wave Races (like graffiti, color, mud, obstacle), some races want to allow a runner to transfer for free even if the price has gone up or if the runner originally signed up with a coupon. You can now chose this option with a simple checkbox under the Participant Management section.