Can a reverse biased diode be driven past its voltage rating but with current limited to few uA
Can..?

Yes you can, as long as no damage occurs. If you limit the current and voltage such that then no damage (to the component) can occur then it won't.

It depends on the power rating of the component how much it can handle. For example a 1 A diode like the 1N4001 has a forward voltage (at 1 A) of 1.1 V so that gives a total of 1.1 W dissipation. In reverse at 200 V at 1 mA that would result in 200 mW dissipation, far below that 1.1 W. So you do not have to limit the current to a few uA, one mA might be safe as well.

A 100 V rated diode is not guaranteed to show breakdown at for example 200 V. It can be at 101 V or 1000 V. The manufacturer only guarantees that breakdown occurs above 100 V.

Basically almost all diodes can be used as a zener diode however a zener diode will exhibit breakdown at a specified voltage. Using an NPN's BE junction as a "poor man's zener" is indeed an option. You just should not rely on an accurate breakdown voltage.