Yes, you can do it simply by using the button's script property, for example:
var tab_index = 1
set("container_id", tab_index)
See Scripting - Open Stage Control
Is it still possible to switch the root tabs at the lower edge of the screen?
With css, yes:
> inner {
flex-direction: column-reverse
}
> inner > .navigation .tablink:before {
bottom: auto;
top: 0;
}