Extreme Programming (XP) is a set of programming methodologies that can be used. You can use some, most or all of them in any combination you want. I know of very few shops that use all of them - pair programming being the least common (this is my EXTREMELY limited survey).
Of course you are welcome to use other methodologies. Ultimately, when you work in a professional shop, the culture will determine what you use. you can always try and change it, but you will generally be working against a lot of inertia.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors