This is all very speculative, and I have probably got most of it wrong, or out of context.
Do not use the information found here to make any decisions about Waze editing.
A segment stores average traverse speed to each of the connected segments, for each available time slot. When split , that speed is split by ??? percentage wise and applied to both new segments, same when stretched, the speed is kept proportionated to the original.
??? Kept proportional to original, or speed is copied to the newly -created segments?
If in understand things correctly, the speed data for a segment is not exactly portable. It's very junction dependent. In other words, it's not just the time lapse of traversing the segment in a particular direction, but what happens as a particular segment transitions to another particular segment. Once you detach and connect to another junction, Waze no longer knows comparative times to turn left, right, or continue. For this reason, there can be strategic decisions in terms of which ends of segments to leave connected and which to move around.
If you are going to lose turn data by disconnecting and reconnecting to the same junction, then that is important to know
by disconnecting and reconnecting to the same junction? I doubt that very much
or at least sorta much