Yes, guitar stools are adjustable, or they should be at least. When it comes to comfort, each person has his or her preferences - for some, it’s about how soft the seat is, while others care more about the shape of the stool and the backrest. Some people prefer a cheap guitar stool or a wood guitar stool. But it’s probable that you always want a stool that allows modifications.
An adjustable guitar stool is good for those that can’t stay put and need to be playing in many different positions. If you’re the kind of player that needs to change the body position every now and then, make sure that you can change the height of the guitar player stool and of the backrest too.
Furthermore, you want to be able to change the angle of the backrest. Don’t forget that the footrest is an important part and if you’re a short person you want to be able to get that footrest higher.