Old houses have always been changed and always will be. If changes are made in the manner and with the materials of the original structure, with respect for a building's place in the streetscape, then there is no reason for complaint. We do need 'house museums', with buildings preserved as if in aspic and open for public inspection. These serve to tell us about our past in a way that the written word can never achieve but the vast majority of old houses have to earn their keep in today's world by providing shelter for people. A lot of people make the mistake of thinking that only the grand houses of the rich and famous are important.
Cottages are just as interesting as any mansion and often a great deal more comfortable to live in.
They are easy and inexpensive to restore and it's astonishing how an old cottage will shine with the right sort of care and attention. You do have to watch what's going on. But often if you tell your tradespeople exactly what you want and explain why it's important to do things in a certain way they will cooperate and become very enthusiastic. The most important thing for the owner is to know as much as possible about their house and its period and to understand the principles of conservation. To give a very simple example, don't let your tradespeople use modern screws or obviously modern hardware in a Victorian building.