As a reviewer, I prefer it when/if I or the client has a question, and the report addresses it specifically in an addendum with a new report date; especially if the report concludes that whatever is requested does not warrant any change, etc.
However, depending on the issue, I can appreciate if the appraiser does not want to go into great detail, etc., etc., etc.
In your case, I would have no problem addressing the request in the report.
Here is what I say:
1. We are obligated to take a look at data presented by the client. That "obligation" (IMO) is not without its limits, but a reconsideration within a reasonable time frame would fall under this category.
2. When I say "obligated" I mean we have a responsibility to look at the data and determine if there is anything in it that warrants a change. That is the function of the reconsideration; not "changing" anything but determining if the data warrants any changes.
3. Once we make are decision, we should communicate back to the client what that decision is. Obviously, if it warrants a change in the original analysis, that communication will be presented in a revised report. In your case, the reconsideration determined no change was warranted (for the reasons you cite). You did this in the email so you fulfilled your obligation as I would interpret it.
4. What the client is asking is if you can put that communication in the report. As a lender, I would prefer it to be in the report because I'm going to use the report as part of my lending decision and the report documents that the reconsideration has been considered.
IMO, Steps #1-3 are what we should do and you've done that.
Step #4 is a business decision, but one I would complete if it were me.
Good luck!