Hello everyone. This question has come up a few times. I myself asked this when I started submitting runs as well.

Yes! You can and should use custom settings for your speedruns. Only cheats are banned. You are allowed to go into the "Customize Weapons" menu and setup your weapons any way you like. You are allowed to go into the "More Settings" menu and set attack strength to anything you want. You can set drop rate to anything you want.

Themes, sounds, skins, coin sound effect are all up to you. You should also disable frame rate lock for better performance. All you have to do when submitting is set rules to custom on the form and you are good!

You just cant use any cheats. (Unless you are submitting a NG+ run where cheats are allowed)

If you have any questions regarding settings and rules, please ask here and I will answer. Thanks!