I started doing that around the turn of the millennium, not because of that but because the mouse cable wouldn't reach, and stuck by it. It's actually very practical as it leaves the right hand free for the numbers pad or a pen.
It's very easy to get used to it, and no problem to switch between different computers running in right hand mode / left hand mode.
The trick is to
- set the mouse to left hand mode
-train yourself that "left click" = "use index finger" and "right click" = "use middle finger"
That way you can switch between modes without thinking about it, your muscle memory will do the work for you.
Nice side effect at work: most people won't mess around with your computer anymore because they'll get confused. It even perplexes the IT guys.