amiga 500 OCS/ECS has its db9 port which can natively manage 3 buttons it would be cool to have at least a 2nd one to be able to jump!
I'd never thought about needing a jump button. And I've never seen a problem with doing it with the up directional key/stick. But your suggestion makes me realize that perhaps some users prefer to jump with a button rather than the up directional key. In fact, in my previous game, The Lost Pixel, I changed the jump from up to shoot, due to popular demand, but with Hundra, wanting to maintain the similarity with the original, I've kept it as it is now.
Changing it now is impossible because the assignable keys in Redpill are already filled with other commands like resetting the character (Shoot 2), going to the menu (ESC), and exiting the game (F2). So I apologize for not being able to satisfy your request. Big hug.