Can I buy a pre - built computer and gradually switch things out and replace them for better things?

I want a new computer right now but I don't have tons of money so i was thinking of buying a pre - built computer and just adding on to it over time. I really want a high end gaming computer in the end. If i buy a computer pre-built (like with an ATX Mid case) would i be able to switch EVERYTHING out of it over time? Including motherboard, cpu, graphics cards, RAM, hard drives, cd/dvd drives, power, fans... everything... and replace them with better things as i get more money? So basically i would be buying a computer, mainly for it's case, so i could constantly upgrade it.