-> as opposed to 'IN WITNESS OF no alteration' or 'AS WITNESS my hand and seal unaltered' (the amendment doesn't refer to the latter)

Note the caps as a conventional drafting opener.

Our inhouse Scrivener-Linguist Notaries (one now or heretofore on ProZ) used the literal translation of 'whereof a /notarial/ act'

Brooke's Notary as the 'Notarial Bible', Sweet & Maxwell -> *any critics pls. quote chapter & verse* : one permutation in no.12.37 being: 'in witness whereof I have hereunto set my hand and affixed my official seal the day and year aforesaid'

and no. 12.38: 'IN FAITH AND TESTIMONY WHEREOF...I the said notary have subscribed my name and set and affixed my seal of office at ..... aforesaid this .. day of ... two thousand and ... '

I think the sentence is to show that there has been no alterations in the document.

1) "dont acte , locution
Abréviation de l'expression "ce dont il est donné acte" ou "ce dont il est pris acte". Elle est généralement utilisée dans le vocabulaire et le lexique juridique et placée à la fin d'un communiqué. Elle signifie que l'information a été retenue et qu'on peut en tirer avantage plus tard.
Exemple : Cette expérience fut désastreuse. Dont acte, oublions ça."
https://www.linternaute.fr/dictionnaire/fr/definition/dont-a...

'The foregoing constitutes legal publication' is given by Termium, among other sources, for dont acte. To me it seems as good a translation as anything for l'information a été retenue et qu'on peut en tirer avantage plus tard.
https://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-fra.html?l...
https://forum.wordreference.com/threads/sous-toutes-réserves...
https://www.proz.com/kudoz/french-to-english/law-patents/121...

Oddly, however, this expression appears only in relation to translation of French documents. I would be tempted to simply gloss over the whole thing, for an adapation, but if the translation is to be set against the French, as well it might, an 'explanatory' translation rather than adaptation might be required.

2) As others have said, sans renvoi means that there are no marginal notes.

In pre-electronic days, a notaire's clerk/secretary typed up a document which was read to the parties concerned. If changes were to be made, they were entered as marginal notes on the paper document and initialled in ink (paraphé) by those present at the same time as each page was initialled.

These days, notaires amend documents directly on their computers, the parties present can see the document, as modified, projected onto the wall of the étude, and can then sign the entire document in one fell swoop by means of the electronic tablet presented to them for that purpose. Consequently there are no longer any renvois / marginal notes. But legal matters being what they are, people cling to tradition and the old ways and instead of simply embracing change feel they have to point out how what is new departs from the practice with what is old.

With that, I shall don my jerkin without laces or toggles or buttons (it has a zipper, you see) and venture out into the cold.


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Note added at 9 hrs (2023-12-31 19:08:21 GMT)
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Re. the suggestion of 'footnotes' elsewhere, a footnote is at the bottom of the page. In all the dealings I've had with notaires, both privately and professionally, the notes are added to the left or right of the body text, hence 'marginal'.

As for the 'legal publication' bit, I think the exact wording hardly matters, for it is probably a conceit unknown to English-speaking legal practitioners and is just there to fill the space. As I suggested, it could well be ignored.

The sense of a French act is a form of documentation which can be historical, a title deed of property or a form of specifically formal writing used to record information and to serve as a legal form of report.
https://www.larousse.fr/dictionnaires/francais/acte/879
A literal translation suggests it's an unsubstantiated report without a reference, or a return. If it's about a court case then it has no resource or possibility of appeal or return, which renders it final.
It's about formalities found in attachments or additions to a document.
A document was produced digitally while a Notary signature is found also in the attachments, in unreferenced documentation.
(A document with an additional supplement or an attachment was produced by a digital system in a Notary's office.)