Though I am not specifically familiar with the Beagle Terrier, I can say that as a person who approves such changes on other types, this would more work and cost than it would be worth. I fly one plane with heel brakes, and dislike them enough, that I do not use them other than for slow taxi maneuvering, or precise stopping while parking. When I train tailwheel to other pilots, I do not include brakes as a method of directional control on the runway. The rudder, or at slow speeds, the steerable tailwheel, will be adequate to maintain the direction of the airplane in suitable conditions. If rudder will not control the direction, you're probably in too strong a crosswind for the type - brakes really are not a good solution.