Unless you really can switch hands at the drop of a hat (which is incredibly rare), the term is cross-dominant or mixed-handed. I prefer my right hand for fine motor skills and left for gross. I have a coworker is who is almost exactly the opposite.
(I do have clear preferences for many other activities, though which activities go left and which right seems pretty arbitrary, and might just be what I got used to instead of actual dominance. Like, I hold my phone on the right hand because it's in the right pocket, but is that a preference, or just avoiding putting the phone in the same pocket as keys/flashlight/etc?)