With this you can easily remap your GPIOs to a virtual keyboard without resoldering it.
but first post :
I have a GameBoy Zero (with Rpi3b) and buttons soldered to the GPIOs.
So sorry, but I don't really get what you did and why it was necessary compared to regular GPIO... but as I said I don't know much about taht.
Besides all links you provide are for retropie, and recalbox is not retropie...
If someone used the same setup goes through here, he might be able to help you, but I don't know more than that.