What's the difference sound wise between
500k pots and 550k pots
Nominal or real value ?
Any component has a tolerance between the nominal and real value. wrt/ pots, the usual tolerance is +/-10%, which means a "500K" pot can read between 450 and 550K. The higher the value (real value I mean) the less high-end you loose (pot wide open - yes even a wide open pot impact your tone), and the difference between a 450K and a 500K pot is audible. The point of 550K (nominal value) pots are they are less likely to be too much under the 500k mark.
And
330pf caps and 0.022pfu
I assume you mean 0.033 and 0.022 ? Because the difference between 330pf and 0.033pf is "orders of magnitude" ;)
Anyway: the higher the cap's value, the lower the cut-off frequency, so a 0.033 cap will start to cut off highs at a lower frequency than a 0.022.
Also there is a tiny capacitor type thing on the volume pot, what is it what does it do? I blindly removed it off all my others to match bkp wiring diagram .
Performing these upgrades is rather familiar to but I never actually educated myself as to the WHY of it all.
cf AndyR's answer. A well designed treble-bleed is supposed to counteract the (inherent) loss of treble when rolling down the volume pot _without_ altering the overall tone. I have yet to try a well-designed treble-bleed, all the one I tried so far made the tone brighter and "tiny" as soon as you touched the volume.
An alternative is the "gibson 50s" wiring, which has other side-effects you may or not appreciate, but for me it works better than any treble-bleed I ever tried.