Little muscle spasms in the whole body (generalized) can be improved with botox?

Probably not. Botox is not great for spasms. It is good for sustained movement such as dystonia, where there is twisting of muscles or spasticity, where there is increased tone. If you have the movements everywhere, the other problem is that you would have to receive injections of Botox everywhere, and this would not be effective. Botox works well when the symptoms are isolated (i.e. One arm).
Not Really Helpful. For You. Botox is helpful for specific muscles that are issues not for general whole body spasms. In fact with your history of muscular dystrophy I would avoid botox because it will make you weaker wherever used.
Unlikely . Generalized will not work. Local & well identified troublesome muscle spasm/trigger points, may respond to botox, but for generalized spasms, no. If there are some local areas that are very symptomatic & other conventional therapies have failed, Botox may be a reasonable option.