https://thesaurus-linguae-aegyptiae.de/lemma/59960 is the Hieroglyph, with translation 'to turn upside down'
https://thesaurus-linguae-aegyptiae.de/lemma/d1981 is the Demotic, where 'to turn over' obviously is a suave interpretation of that. I prefer to stick as close as possible to the original words, which means that for nouns I choose the translation that goes with the verb, which in Coptic - and thus in English - frequently are identical
Five times does the verb ⲡⲱⲱⲛⲉ exist in Thomas, in Logion 35, 48 and 106. Never as noun, although 66 will have it:
66. IS said: go on, show me the stone, this one they have rejected, viz. they who build: he is reversal of envy
I'll include credits to Eddie C in the footnote to 66
Alternatively, ⲡⲉ could be read as definite article, such as we also find ⲡⲉ in Thomas 6, 9, 57, 60, 65 and 76.
And then it would read:
66. IS said: go on, show me the stone, this one they have rejected, viz. they who build: he the reversal of envy
The overwhelming preference for ⲡ- in Thomas is selective, and e.g. Philip has ⲡⲉ by default. But in Coptic, ⲡⲉ is the so-called nexus pronoun / copula, see e.g. Layton $279
(Bentley Layton, A COPTIC GRAMMAR With Chrestomathy and Glossary, Sahidic Dialect, 2000, Harrassowitz Verlag. Wiesbaden)
"Opposite" is what I get from this word. Inversion, reversal, a genuine turning upside down as in the house of Thomas 35: a complete turning around of an imaginary chess table, switching sides, swapping the pieces.
Although I am now inclined to take the verb in 35 intransitively, and will translate ⲧⲟⲧⲉ ϥ ⲛⲁ ⲡⲱⲱⲛⲉ ⲉⲃⲟⲗ ⲙ̅ ⲡⲉϥ ⲏⲉⲓ with "Then he will move out of his house" instead of the current "Then he will turn outward [dop] his house".
Thanks again Eddie, I will also put this on my list of unattested - apparently it slipped through.
I certainly hope you continue playing around with Thomas!!!