Transistor substitutions.... I still don’t get what you can and can’t get away with.

[Paradox916]

Could someone shed some light on this for me the 2N3904 has higher voltage tolerances, so it would be ok to sub this for a BC550C without any issues? Of does all the other differences and characteristics make it an incompatible swap? And this would be a substitution in an lsosceles boost. Would there be any noticeable sound difference... or would I fry something? I’m still learning.