Someone losing their dominant arm

Question

There are some practical differences between righties and lefties in halacha. What happens if someone loses their dominant arm? Do they gain the halachic status of being dominant with their other arm or not? For example while a left handed sofer can write tefillin with their left hand, a righty cannot. If a right handed sofer lost his right arm, and taught himself to write with his left hand, would he be allowed to write tefillin with his left hand?