Q: Is it possible to revise a schematic diagram of the experimental setup after receiving the email of my article proofs?

There might actually be two elements to consider here. One is that of the diagram for this paper. The other is the matter of the other paper.

Based on the minimal details provided here, it may seem that the two papers are an instance of salami slicing, the act of breaking up a larger paper into smaller papers to increase one’s publication count. This obviously is an unethical practice. The one instance in which this would be okay to do is when the research is large enough to warrant multiple publications. You would be the best person to decide. As you are anyway mulling over the schematic diagram, and although the second paper is so close to publication, now might be a good time to think over the situation of the two papers.

Coming to the query of the schematic, that brings up questions of its own. How large is the diagram (and therefore, the experiment)? Do you plan to make only cosmetic changes, such as shading and shape? (That may make the two diagrams look somewhat different, but not significantly so.) Do you plan to make changes that might impact the flow of the experiment and possibly even the results? (This obviously may not work.) And all this gets further complicated because your paper is at the proofing stage, when only minor changes (such as spellos and punctuation) are okay to fix.

So, here’s what we suggest.

• As your previous paper is already published, you can include this diagram in the present paper but with citing the previous paper. This will help you avoid the other issue of self-plagiarizing.
• Based on what you decide on the matter of salami slicing, you may need to share this information with the editor of the present journal, before the next (and actually, final) stage. Based on what they suggest, you can proceed accordingly. Of course, this might mean that your paper gets stalled a bit (or in a worst case, not get published), but this would be the ethical thing to do. But again, this needs you to step back and think this situation over.

For help on the various points we have discussed in this response, you may refer to the following resources:

• Is it self-plagiarism if I use an image from one of my previous papers?
• Can I replace an image at the proofing stage before publication?

As you have some publishing experience, and although it is a bit long, you might also find this course helpful: How to avoid retractions and publish ethically

Hope that helps. And all the best for your next actions.