You can just ask a mod to change your screen name (one that's seen publicly) for you; unfortunately I don't think it would be possible to have your original username changed. (although i'm not a mod so idk for sure) You may need to use same original username to login but if you have your screen name changed, then others wouldn't be able to know your original username unless somebody hacked into the site and stole a bunch of data and Doxxed you.
As for email associated with the site, again I don't know-a mod would be more likely to be know more than I do regarding these issues. However, I know you can chose to keep your address private and not share it on your public profile.
Frankly, though, it's really easy to draw associations and connections between different accts on different sites and eventually find out who is behind the screen name without hacking into servers or simply searching for similar screen names. Oftentimes I find that one's own writing style, photos/media of interest posted, etc. to be a wonderful way of incriminating/implicating one's irl self (but that's just me). For example, you just stated that you are Donothello27, and therefore the ghost is gone-we know who you are yet again. Nothing is private anymore. Anything posted online, whether in the shallow or deep web, can still be traced right back to your doorstep with enough time and effort spent by of the inquirer on the hunt for you. The real question is whether or not you've implicated yourself in activities significant enough to warrant such an extensive exhaustion of LE resources; it costs lots of time and money to put the pieces together and big fish fry better than guppies.
No Worries,
-Mangrove