Anyone ever make a fanfiction while they read?

I'm not finished with the question yet. What I meant is, anyone ever replace the characters in a manga/hwa/hua and imagine it with other characters in different story? I'm sorry if that's confusing, let me give an example

For example, I recently kinda imagine Into The Rose Garden but with Harry Potter ships, that is James Potter x Severus Snape. Whereas James Potter as Kloff, Severus Snape as Aeroc, and Lily Evans as Rapiel. I don't know if you've read ITRG before, but I kinda like to see obsessions and prides twisted with love between James and Severus, consider their past ㄟ(≧◇≦)ㄏ

So...is it just me?

P.S. I sincerely apologize if I ruin your favorite Harry Potter story OTL