There is a long discussion here on the forums about static and dynamic targets, and I think that David Chart’s suggestion is a good one that has a lot of support in the existing text.
I think it is a reasonable conclusion that Individual and Part can be either static or dynamic for any given spell, just like containers can be, and that this is chosen at spell invention. I think that Group should be permitted to be dynamic, but agree with David’s conclusion that the text as written explicitly does not permit dynamic Groups.
I do, however, want to disagree with some of the other participants in that thread and contend that we have explicit support for dynamic Part target in the text of ArM5:
A pit opened for duration Moon with a Perdo Terram spell cannot be filled in with earth for that period; any more earth dumped in it is destroyed as well.
ArM5 p.112
The example spell that we have for opening a pit in the ground is Pit of the Gaping Earth, which, while Momentary, is Part Target. I believe that these two statements together provide a strong basis from which to say that Part at least can be dynamic rather than static.
It’s a bit fuzzy I think as to whether that actually counts as a dynamic target. However, Definitive Edition does have one explicit example of a dynamic Part target - Lungs of the Fish. That comes with rather a large caveat:
Lungs of the Fish
R: Touch, D: Sun, T: Part
Requisites: Auram
Turns water into air as it enters your lungs, allowing you to breathe water as you do air. This spell puzzles Hermetic theoreticians, as it behaves like a dynamic container target despite not being a container target. All known attempts to create analogous effects have failed, even though analysis of this spell has not revealed any sign of non-Hermetic influence, or integrated experimentation. Most magi just point to it as an example of how Hermetic magic is not fully understood, and get on with their lives.
Thing is, it actually can be recreated trivially with Room Target, but this is a magnitude higher.
I think that the best rationalization is actually that Lungs of the Fish actually has a Special Target following the rules on changing RDT parameters for formulaic spells and it is actually a Box Target equivalent to Individual with the +1 magnitude custom target tax, and that the rest of the Order fails to create analogous effects because they see the spell level and assume it must be Part Target since it's the same, then fail to recreate it because of that.