Modify ball joint for wall corner

I have an existing 3D-printable part set in STL format that needs a few quick tweaks. This is for a ball joint that I want to modify for use in a corner. The current set has 3 pieces:
1) The ball
2) The threaded wall mount
3) The tightening nut

I would like the below 4 edits made, but importantly NOTHING ELSE should change with the parts.
1) For the threaded wall mount, I would like the back to have a 90 degree wedge shape so it fits into the corner of a wall (reference: https://cleanshot.com/share/hN13TYPh5xXzgffy5v3F)
2) Also for the threaded wall mount, I would like the inside hole to have a countersink for #8 drywall screw (Ø4.2 mm screw, Ø8.5 mm countersink major diameter), so the screw head sits flush with the surface. Reference: https://cleanshot.com/share/yqZjgQBTM59b0gqpTd95
3) For the treading nut, I would like to add a knurled texture. Reference: https://cleanshot.com/share/Gr8CgFWtSjFN2SgNwLVm
4) I would like the ball arranged inside the threading nut, so it prints nested inside the nut (reference: https://cleanshot.com/share/ylyDMt9st882MDYrgT5P), AND increase stem base diameter, with a target clearance of 0.15 mm radial between stem base and surrounding captive nut/cavity. Minimum acceptable clearance: 0.10 mm radial, provided the joint remains printable in place and can be broken free after printing. Reference: https://cleanshot.com/share/zcC3CwjKDbz53jrb84tM