how to label changing postures?
The whole point of using words to note is that you are labeling the thing you are meditating on in accordance with what it is. If you are rising up to stand, you aren't actually standing at that time, so it is inappropriate to note it with the word standing, as you want the noting to be simultaneous with the object itself.

Ajahn Yuttadhammo explains some of the principles of the labeling being simultaneous in his section on walking meditation on page 16 of his meditation booklet where he writes:


  One should make the mental note   at the exact moment of each
  movement,  neither before or after the movement.
  
  If the mental note, "stepping right",  is made before the foot moves ,
  one is noting  something that has not yet occurred. If  one  move s
  the  foot first and then note s,  "stepping right", one is noting
  something in the past. Either way,   this cannot   be   considered
  meditation,   as   there   is   no awareness of reality in either case
  .