Everyone "stretches" their strings. Yup. Even those of us who do not grab the string and shake their instruments over their laps while wearing a striped cap.
What is "stretching" the string? It is simply removing the slack that is stored between the pegs and the nut, around the peg itself, and any that might be stored between the saddle and the tailpiece.
Multiple tunings do the same thing. It just takes longer.
Does "stretching" cause the string to wear out faster? There is a lot of opinion on this one. You would think that the oils, acids, skin, and grime that is placed on the strings every time they are played do in a set of strings faster than any effects due to "stretching". Some suggest "stretching" causes metal fatigue. That kind of fatigue is usually the result of long term exposure to abuse. It would be interesting to read some scientific evidence on this.
This video shows an extreme version of the technique. A few quick tugs and retuning is all that is needed. You might have to repeat it a couple of times to lock it in.
None of this will harm a bass guitar neck. That includes using the yo-yo technique demonstrated by our intrepid expert.