Theoreticly, yes, though I haven't tried it. I'm not even sure if we can manipulate hardpoints on the fly (other than attribute changes).
yep, just putting both in the same place and changing values might work
for example, switching between 0 and full charge and recharge rate as you click the button, say, when you're in phaser mode, the cannon stays discharged and doesn't recharge. when you switch to cannon, discharge the phaser and set the recharge rate to 0.
even the icons will change with the weapon.
I tried to make HP changes in-game, but it seems very hard, if not impossible.