What exactly constitutes a visible change to the game state?

example:
a counter being placed on a creature?
a life total change?
a card draw?
a discard?
an application of a continuous effect that modifies an object's characteristics?

if I annouce a target for the trigger on Cryptoplasm, at what point do I have to announce whether I choose to copy the target object or not?

eg. Mirror Gallery is on the field and Cryptoplasm is currently copying Phage the Untouchable, my upkeep occurs and I announce the trigger's target is Swans of Bryn Argoll (say my opponent only has 2 cards left in his library)

when do I have to say whether I chose to apply the copy effect or not?

(in this example, I suspect it'd be in the declare blockers step if I attack with C-plasm because if I do apply it, the creature has flying, but what if I don't attack?)

Edited Todd Bussey (March 14, 2013 02:20:20 PM)

Visible change is essentially as it says. A counter being placed somewhere, change in life total, whether something is tapped or not, flipped, unattached, phased in/out, face up/face down etc.

Your specific question is confusing though. I think what you are trying to ask is - “How long do I have before I've forgotten the Cryptoplasm trigger?” Which because it targets as per the IPG GPE - Missed Trigger section -

A triggered ability that requires its controller to choose targets (other than ‘target opponent’), modes, or other choices made when the ability is put onto the stack: The controller must announce those choices before they next pass priority.

You must announce the trigger before you next pass priority. If you announce it, you have to make the choice on resolution of the trigger. The trigger is at the beginning of your upkeep so you have until you draw a card to announce the trigger and what you are targeting, then after any responses, you make the choice to copy or not.

Originally posted by Todd Bussey:

eg. Mirror Gallery is on the field and Cryptoplasm is currently copying Phage the Untouchable, my upkeep occurs and I announce the trigger's target is Swans of Bryn Argoll (say my opponent only has 2 cards left in his library)

when do I have to say whether I chose to apply the copy effect or not?

When the trigger resolves. Once you've declared a target, you've acknowledged the trigger so there isn't any ambiguity over whether or not you've forgotten it, so ‘visible change to the game state’ isn't relevant.

If it gets to Declare Blockers and there's confusion over whether you opted to actually copy the swans, I think it's strictly GRV/FtMGS as I don't think it falls under CPV. There's no official default shortcut that assumes ‘Place trigger on the stack targeting X’ implies ‘and I chose to copy/damage/steal/whatever’ but I'd argue it's a generally held assumption, so I guess the precise wording of the target would be relevant here. Otherwise if you don't say one way or the other you'd be assumed to have failed to resolve the trigger on the stack correctly.