I wanted to lengthen the stem of a pair of tied chords, but it didn't work as expected. After some playing around, I found that I cannot tweak the properties of a chord represented by q (repeating the previous chord), but that the tweaks on the original chord get carried over. This example shows the possibilities:
%%%%%%%%%%%%%%%%%%%%%% \version "2.23.80" { \clef bass \voiceTwo <a,^~ a,,_~>2 \tweak Stem.length #15 q8 r4. | \tweak Stem.length #15 <a,^~ a,,_~>2 q8 r4. | <a,^~ a,,_~>2 \tweak Stem.length #15 <a, a,,>8 r4. | } %%%%%%%%%%%%%%%%%%%%%% This may be logical in the code, but it surprised me in practical use. Paul