Slater
Headphoneus Supremus
Do you guys think a ZS5 -> ZS3 reshell is possible considering the size of the components?
Would it screw with the accoustics?
Not enough room in the ZS3. There's only enough room for at most a 9mm DD driver according to my measurements when I had the shells apart (the stock driver is 8mm, so there is room for a larger driver swap, but 9mm is max). Also the nozzle is awfully small to fit a BA driver and still have enough open room in the channel for the sound from the other drivers to pass.
A better donor shell would be the ZS1/ZS2/ZN1. It's very comfortable to wear, and even has dual sound channels for better frequency separation. It is easy to open, and has enough room for 1-2 BA drivers (in the shell not in the nozzle) and a crossover.
Another option would be to rework the ZS5 shell. Sand it smooth with a Dremel and smooth/fill in the thin spots with Bondo and repainting. It won't look sexy and CIEM-ish like the ZS3, but it won't have the sharp edges anymore.
Finally, there's tons of info at the Home-made IEM thread (https://www.head-fi.org/f/threads/home-made-iems.430688/) You would fall out of your chair seeing what those guys have made, casting their own CIEM shells using readily available materials.