As far as martial arts go, is there really anything you can't learn on your own (alone in the sense that you don't have a proper instructor, not that you don't have a sparring partner) besides things like how to do a proper horse stance and silly things like that?
When I think about it, it just seems to me like most martial arts in general mainly teach people improve their reflexes, reaction time, and coordination, which are all things one can do if they use their common sense when training. Things like joint-locks and grappling techniques to me seem like they could be self-taught from either watching videos of others, reading a martial arts guide, or even just coming up with stuff on your own, provided you have a partner you can try your ideas on.
I guess theoretically it is possible, as that is how people come up with new styles of martial arts, but what do you think?
To your original question......to do so IMO would be wasteful. As others have said without an instructor to show you the little things you are doing wrong or right it would hinder you greatly.
I'm an Instructor of Ju-Jitsu in which we use joint-locks and grappling extensively these techniques are dangerous and are finely taught, tuned and applied and without proper instruction in joint manipulation you seriously run the risk of destroying much needed parts of your and your partners body.
My advice is do not do it, bad things will eventually happen.
Michael