A global command that says “This row lasts X ticks longer than normal” …and of course the counterpart “Pause for X rows” which would be same except it would multiply parameter (in ticks) by current ticks-per-row value… these are unfortunately kind of missing when doing stuff that changes tempo a lot 
(Random thought: maybe dedicate a letter for “dispatch” to commands/effects that take only one digit parameter? like the S?? commands in ST3/IT/Schism/modplug/related trackers)
ZK01, ZDxx?
Oh, “duh” about ZDxx, it was in plain view on tutorials.renoise.com =)
…but ZKxx sets the ticks-per-row value, it doesn’t just add “xx” tick duration to the current row. Works, but more of a hassle to play around with.
It would behave just like ZDxx, but with much greater precision.
If you want to delay a row for 5 ticks, that would be ZK[current tickrate]+5, which is indeed a bit more hassle, because you have to keep track of what the current speed-setting is and setting it back to it the next line.
It’s not too hard to script that though…
The only real major disadvantage is that other tick-depending commands behave differently when the tick rate changes (Like retrig) so you also have to customize the value of those commands to the temporary new tick-setting.
since the new concept of Ticks Per Line has been introduced over the old Speed concept, raising the number of Ticks Per Line won’t make the line last longer so, unless I’m missing something, a combination of ZDxx and ZKxx will not have a different effect than using ZDxx alone
I could say this still works with old unupgraded Renoise songs, but then i should in that case refer to the old pattern effect commands…
…so, in conclusion…
feature request: a command for adding “x” ticks duration to current line 
(btw it-alien is right, with the new speed/tempo setup, ZKxx doesn’t change the duration of anything, just the tick precision per line)