Isn't all choice a form of altering conditioned behavior, the tweaking of inputs as compared to stored prior memory ?
All dogs have four legs, but not everything with four legs is a dog. And what do you mean by "tweaking of inputs" with regard behaviour? The behaviour is the output, not the input.
The brain can make wrong guesses based on conditioned behaviors.
Where is the "guess" in the examples you gave? Is your assertion that plants "guess"?
Is threshold behavior ( mechanics) a form of choice or must choice always be a conscious act?
No, choice need not always be conscious, and whether threshold behaviour is a "form of choice" depends on how one defines
"choice".
How about homeostasis, where the subconscious part of the brain maintains biochemical balance in concert with the bacterial symbionts of the organism?
What about it? Is my thermostat turning on and off an example of "choice" given that it maintains a thermoequlibrium within my house?
It is a matter of interpretation, no?
Not really. More a matter of definition: what does one mean by "choice", by "freewill" etc. I would suggest that once one has arrived at a definition they try to see what they are allowing to have "choice", "freewill", and whether something as simple as a thermostat could be said to possess such. If so, is it really the definition you want to go with? If it does allow that, is it particularly useful?
What are other definitions for choice?
Merriam-Webster
Ah, yes, the self-referencing definition of "choice". All that definition does by using the words "choosing" and "chosen" is show how the noun relates to the verb (present participle) and adjective formed from its root. It is nothing but a matter of liguistic form rather than meaning. At no point does it actually explain what "choice" means without effectively referring to itself. So not a very helpful definition, I hope you can see? "
X means the act of opportunity of Xing or the thing Xed."
So, since it begs the question: without simply using the same root, how are you defining
choice? Or
to choose?