How do you feel about authors like E.L. James modifying their fanfics into stories of their own? It's honestly not something I have a solid opinion on, so therefore I don't have an answer on whether I myself should do it or not.

1. In theory, I don’t mind. As a former fanfic writer, I know just how much a fanfic can change - to the point that in a lot of cases, the original work is really only inspiration for the resulting work. 

2. In the specific case of E. L. James, I find it appalling, for numerous reasons. She stripped Twilight of what actually did make it an interesting, appealing story. And I’m not a fan of Twilight by any means - I have my problems with Meyer. But there were a few aspects of Twilight that were genuinely done well. (That’s a post for another time. I won’t go into it.) James stripped what depth the characters in Twilight did have away and made them shallow, barely-there copies of their former selves. 

I think if you do turn a fanfiction into your “own” story, you have to add yourself into it. Not just your sexual fantasies (Sorry, EL), but something meaningful. Maybe that means wondering “what if” and going from there. For example, what if Harry’s treatment by the Dursleys had made him a power-hungry Voldemort 2.0? How can you use that as a starting point for a story of your own invention?