I have used the gentle tug at the 12th fret for many years. I use two or three fingers under the string so the angle is not as sharp. the process is 1. tune to concert pitch, 2. tug on the string, and 3. retune to concert pitch.

I think I picked this up from watching Tom Rush change a string in mid-concert once. The concept made sense. I figured it stretched the strings better than just tuning up a half-step to stretch it and then retuning to concert pitch.

The guitar, which holds tuning well, usually stays on pitch from there on out.

A note of warning: I did break a 10 gauge string once doing this.

Speaking of changing in mid-concert, one of my strongest memories was watching Hootenanny on TV and saw Paul Prestipino (I hope I have that right) change a string in mid-tune without stopping his playing. I think he was backing up the Chad Mitchell Trio.

Roger in Baltimore