Can you appeal to the associate editor when given unreasonable requests for revisions? We submitted a paper and got two rejections (from reviewers 1 &amp; 2) and two acceptances (from reviewers 3 &amp; 4) after the first round of revision. Now we have received a letter from the associated editor asking us to again revise the paper, and to include a response letter addressing the concerns of reviewers 1 and 2. Hence, the paper is not rejected or accepted. 

We feel reviewer 1's comment to include a new case study is not reasonable, and reviewer 2's comment fundamentally changes the problem structure. We explained our reasoning in both cases in detail in our original response letter (especially in response to reviewer 1). 

Is it reasonable to appeal to the associate editor at this stage (i.e., before rejection)? 

UPDATE: The paper got published in the next revision. We took a middle path strategy: I wrote directly to the associate editor and briefly discuss my objections with the reviewer 1 &amp; drafted my response letter to reviewer 2.
Not a journal editor, just a researcher.

I would respond to the reviews directly. You don't have to accept all the proposed changes; you can simply say "We feel this fundamentally changes the problem structure...." and give a paragraph or two on why.

That said, I might also reply to the AE. This can be very brief, something like "Our updated draft and responses are submitted. Note, however, that the two negative reviewers requested significant changes that we do not feel are appropriate; we reiterated our objections in our response." That way there is no formal appeal (yet), but perhaps the AE will review more carefully if the reviews come back the same as before.