On Race Space, transfers and deferrals work the same way. In both cases the participant exchanges their entry for credits, which they can then spend on re-entering another of your events, or on entering someone else.
Why it works as credits rather than a direct swap
The participant does not have to decide immediately where the entry goes. They keep the credits on their account until you launch another event they want to enter. That removes the pressure of finding a replacement date or a replacement person at the moment they drop out, which is why the credits system holds up better than a direct transfer.
The credits can only be spent with you, on your events, and they remain valid for 12 months from the point the entry is exchanged.
What you can control
Set this up per event, in the Racer Services section of the Event Creator. The parameters you can set include:
A cut-off date, so credits can only be taken up until a certain point before the event.
A partial credit value, so participants receive credit for only a portion of what they originally spent rather than the full amount.
Credits expire 12 months after they are issued regardless of the parameters you set, so a participant who drops out cannot hold a place indefinitely.