To avoid affiliates from changing their referral link you can simply toggle off the Referral Codes option in your program's settings.
To customize affiliate referral links you need to move on to 'custom links' and 'custom tracking method'. There can be a couple of situations in which you might want to change this:
- Since the referral code section can be easily customized by affiliates, you might want to avoid this to happen.
- You want to get rid of the ?ref= part of your affiliate links.
Note: To set up custom links, your developers can refer to this article.