>I was wondering how many Khz you can change the crystal's frequency
(F <
>10Mhz) with changing the caps...


They're not designed to be changable at all. That's the whole point of
a crystal.
Ideally, it wouldn't be possible to change them at all.

The old military HF xtals were in little boxes, and you could open the
box, take out the rock, and grind it with Ajax, or rub a little solder
on it, and alter the frequency.