you can do that on Mac (if you first set the nudge keys to option+arrows).. for example. that's
Join via page down key:
that's possible on Mac too.
if you set right-click to show context menus then it won't repeat commands. (and actually, iirc, the earlier versions didn't have this setting.. you couldn't repeat commands on mac with right-mouse button.. this preference was added later to be more in line with Windows Rhino)
so maybe just switch OS?
or maybe these options are also available on Windows?
regarding the space bar--
what do you want to change it to? the space bar in Rhino is the same thing as enter key.. and to me, it makes sense in a command line driven application because the enter key is off to the side so there'd be a whole lot of reaching across the keyboard with the left hand if spacebar was something else.
but you'd rather it be what, exactly?