If you have a copy of the C++ code, the contents of src/protocols/moves/RotateJumpAxisMover may be valuable. They show (well, not with enough comments) how to separate the two “stubs” (coordinate frames) out of the Jump, modify one of the Stubs, and then reassemble it into a Jump. Maybe you need to take the downstream Stub of pose1/jump1 and insert it into pose1/jump1 while leaving the upstream stub of pose1/jump1 unmodified. (By upstream and downstream I mean w/r/t the direction of folding in the atom tree).
I have no idea if this is applicable in python or not.