I am able to cross my eyes when I want. Can doing this somehow damage my vision by giving me strabismus?
It is actually a pretty common myth that crossing your eyes too much or for too long will make them get stuck that way. Crossing your eyes does look very similar to strabismus which is an actual medical disorder where the eyes are crossed and it does need to be treated. Strabismus is not voluntary, compared to what you are talking about, which is voluntary.
Why doesn't crossing your eyes cause any damage?
Now, that I've gone over the what, I'll go over the why. Many times throughout the day, you will cross your eyes on purpose, but won't actually think of it as crossing your eyes. Crossing your eyes is the natural reaction to looking at something very close to your face. We need to angle our eyes so we can see objects clearly at a close range. This is essentially the same exact movement you would make when crossing your eyes. Our eyes are designed to be able to move up, down, left, and right, and, while it may not seem like the most natural eye movement, crossing your eyes voluntarily is completely normal.
There is a potential for temporary disorientation, pain, or possible blurring if you cross your eyes for too long, but it would only last a short amount of time. This is because you would be putting more strain on the muscles in your eyes, in this case it would mostly be your medial rectus muscles. All you need to recover from this is to just rest your eye muscles, just as you would after a workout.