Totop script and function is part of core gantry5 - so I won't be changing that. So, you can't change the easing on totop or add the #.
What I would suggest instead is that you just create your own customhtml particle instead of using the totop particle in that just put...
<a href="#" alt="To Top">To Top</a>
Then my smooth scrolling script will apply instead and you've be able to do everything you wanted.