They're editing your work to help you visualise what you can create with your piece. If you edit that and claim it as your own work without their permission, you're simply being very dishonest. I've known of C&C edits that are so simple that it would be incredibly unfair to disallow the original artist from simply using it - however if this is the case i see no reason for them not to edit their own work to match, because at least then the technique or idea will be more memorable and understandable to you for when you perform it again.
If the edit they perform actually goes beyond your abilities, but they still allow you to use it as your own work - then consider how this will help you. The reason you're here is to learn, so simply using someone elses work is going to severly burden your mission!