User blog comment:Observer Supreme/Free Modification Human vs. Modified Humans/@comment-26058050-20170509152011

It is possible for Modified Humans to be altered or modified by devil fruit powers. This was shown (and spoiler alert for those who don't read manga), after Pudding told Reiju what her family plans for the Vinsmokes, where she altered her memories thanks to her DF power.

As for the Ope Ope no Mi, that works on the human body itself, and unknown if works on the psyche, though it could be possible for a brain surgen to be able to perform that level of power if they had the Ope Ope no Mi. So I do believe that it would be able to modify modified humans.