Learn English – word for someone that is impacted by change

The first word that came to mind was tentative (unsure; uncertain; not definite or positive; hesitant).

After reading more carefully, I think a better word to use would be proposed (to put before oneself as something to be done; design; intend), as you have both put this collaboration before yourselves as something to be done, but it is still subject to confirmation.

Would you like to tell me more about your ideas for our proposed collaboration?

Consider shock (Oxford Learner’s Dictionary):

[countable, usually singular, uncountable] a strong feeling of surprise as a result of something happening, especially something unpleasant; the event that causes this feeling

As you have a number of “unwelcome surprises” in your text I would reserve shock for the really bad ones. Here are some examples of actual use (my boldface):

Prokofiev had a shock waiting for him in Chicago regarding Oranges. After arriving in town on 31 October he wrote to Johnson requesting a meeting to settle their disagreement "peacefully." The letter he received in return on 2 November did not contain anything about an appointment, rather it bore the news that two weeks ago a telegram had been sent to him in France stating that Oranges had been canceled permanently.
[Stephen D. Press, Prokofiev’s Ballets for Diaghilev, 2006.]

Our return to England was homecoming in many ways, but there was a shock waiting for me when we reached the hotel at Rye. I was handed a cablegram: “Don't come home. I am in good hands. Mother.” The rest of the day was frantic. Heart Attack? Stroke? Paralysis?
[Doris McCarthy, Doris McCarthy: My Life, 2006.]