I upgrade my bikes to make them work well for what I want to do. I could ride my miele road bike the way it came with downtube shifters and a 52/39 and corncob out back but I don't ride like a roadie nor am I built like a racer so I have a triple and 11-32 out back so I can ride it on 200km rides and still walk afterwards. Personally I usually stop if I have to modify a perfectly finely painted frame by putting new braze-ons or something like. If it's bought as a frameset then I think any kind of wheels and groupset are fair game. If the paint is damaged or something then I'd go ahead and add canti posts or whatever else one might want, it's better than just sending it to the scrap yard like a lot of old bikes end up.