How to change origin of a bone without affecting how the armature works?

i know how to change a object’s origin. but how do i change a bone’s origin so that for example i can rotate the bone around a cube?

It sounds to me like you should duplicate that bone, move it to the center of the cube, clear any constraints on your duplicate, disable deform on your duplicate, and then parent your original to the duplicate. Then you can transform this new, sandwiched parent to rotate about a different origin.