If the green information bar can't be disabled, you can always shrink it. Just move the cursor to the right edge until the left/right arrows appear, then move to the left to shrink its width until it is as small as possible. On my widescreen monitor, I can shrink it to about 10% of the screen width but no smaller. (I usually reduce the green bar to 25% screen width at the start of a session anyway.) And you can use the mouse to drag the remaining small green bar to a less obtrusive position on the screen.
Be aware, however, that GSX isn't the only utility that uses this notification bar. I suspect that is why (GSX) appears at the start of all GSX-initiated posts, so you can tell which program is sending the message. If you press Shift+E to open/close the main door with or without GSX, you'll see "Main exit opening/closing" and "Exit open/closed" messages there. And other add-on programs like REX use it as well, although REX has added an option to disable it.