Motorola vt71
 

In the vt71 Motorola there is 2 300v 120uf capacitors was wondering if those caps can be replaced with 100uf with no working problems being these old sets already have the so called 20-30% built in. If this can be used is there a difference between any other capacitor and a disposable camera electrolytic capacitor rated at 100uf 300-330v

Do you have any way to check the true value of the 100 mfd capacitors? Most electrolytics are allowed +50% -20% from what I have seen. The total B supply current is 110 milliamperes so I don't think there would be a problem.
Like you mentioned, these sets have a pretty wide tolerance in parts.

I measured the cap it’s at 102uf

I have 2 450v 470uf in there now which was supposed to be temporary but I never changed them I think it’s time to get them out befor it takes out the b+ diodes.

Or the ballast!

It'll probably work fine. B+ may be slightly lower, but line voltage today tends to be slightly higher so it'll probably be a wash.

Depending on physical size I might be concerned about camera flash caps having poor life rating in continuous filter duty, but without seeing a datasheet it's hard to know... Not many people run electrostatic sets for more than 30 min every few weeks so even if life isn't long it may not matter.