If you're using 8.1.22 or newer, you can control this while making use of the stylesheet.css resource.
I applied the two following rules to my stylesheet:
#centered {
justify-content: center;
}
#space-around {
justify-content: space-around;
}
These two rules target two Horizontal Menu components with meta.domId values of "centered" and "space-around".
This is how they appear in a session (centered on the BOTTOM, and space-around on TOP).
Please note that these two examples have relatively few items, and it is unclear how the left/right scrolling options will work with these settings in place as the rules would also be applied to those proprietary scrollers.