I can confirm that the mana regen trick did used to work. They eventually fixed it, but back in the days when mana regen was pretty minimal and the numbers themselves pretty low (and frankly, you had a hell of a lot of downtime in which there was nothing to do *but* watch the numbers), this absolutely worked. I used to time uses of my Deepwater helm (10 second cat of daring) to heal me, whilst still getting sitting regen every other tick. You could easily tell whether you got like 3 mana or 12 (or whatever the med rate was at the time), so it's not like you could make a mistake with this. It did work. It's also why mounts were such a huge deal for casters. While on the mount you were always considered to be sitting. So as long as you didn't have autoattack on, and weren't actually casting a spell at the time, you'd get sitting regen when the tick came.
They played around with various fixes for this, but eventually just switched to the OOC regen system and made the whole thing moot.