Oh yeah: and plus I mis-read your second question, problem where your soldering heat starts acting on the shrink tube, before done soldering wire, so you can't slip it over the recent connection.
WHY, can't you just prepare the cable, as there is room to strip that a bit more. So your heat shrink piece is way back away from soldering heat. Then, simply slip it over the newly (cooled) joint, and plus you could, optionally, place a large diameter piece of shrink wrap over the whole thing, after each individual wire is done, with soldering and covering w the shrink.
That sounds like overkill, but the large outer shrink segment gives a neat, finish appearance to your cable.
It may make cable stiff along there, if that's OK.