Cable Sleeving Guide

[JaccoW]

Yes it can be stretched. I use those bent needle-nose pliers for it. If you are carefull you can stretch it to almost twice the size, but expect to have a few broken heatshrinks flying through the room.

The problem with the 24-pin cable is that it is relatively broad at the end of the cable. When you shrink it it will probably slide up and reveal the cables.
You could however sleeve just 10cm of the individual cables (or group them by, lets say four together) and use a larger sleeve single for the rest.