Hi: In order to make ctrl+A to echo what normally the Home key does, which is my goal, using xmodmap, I would first have to make ctrl the Mode_switch key, that is

keycode 105 = Mode_switch Mode_switch

The problem however is that the key then won't work as the normal ctrl key anymore. Is there a means to attain the behavior described above?

Do you have a Super (aka Windows) Key? That's the one to use for making your own shortcuts. For Home, End, Up, and Down I'd suggest Super and the cursor keys.

If you also lack the Super key, do you have something useless that you could redefine: Scroll Lock, Pause, Menu? I mentioned the evdev file in my reply to your other post, and gave the wrong address for Slackware: I think it's in /etc/X11/xkb/. You can alter things there, so changing
<LWIN> = 133;
to
<LWIN> = 105;
and commenting out
<MENU> = 105;
would make the Menu key into a Super key.