Ciao Stefania,
sembra trattarsi della possibilità, molto ben codificata nell'ordinamento US come si può vedere dai link riferentesi a diversi Stati degli USA, di porre vincoli conservativi e di salvaguardia (spesso di natura paesaggistica ma non necessariamente) dai proprietari di beni immobili all'atto di cederli per contratto o di trasmetterli per via testamentaria. L'acquirente o l'erede, pertanto, subirà una limitazione dei diritti astrattamente esercitabili sul bene immobile acquisito, per via del gravame istituito dal precedente proprietario.

Nel tuo caso ti propongo di tradurre le 2 occorrenze in 2 modi leggermenti diversi:

1°) "...will be made subject to the terms of the Constitution in the form of a restriction." = sarà effettuata nel rispetto dei termini dell'(Accordo di) Costituzione sotto forma di vincolo / mediante apposizione di vincolo

2°) "The Purchaser...acknowledges, agrees and undertakes...that the Constitution has the form of a restriction in a document " = L'Acquirente...riconosce, accetta e conviene in un documento che l'Accordo di Costituzione assume forma di vincolo / ha natura di vincolo / possiede valore di vincolo


Riferimenti:

A conservation restriction refers to a right appropriate to retaining land or water areas predominantly in their natural, scenic or open condition or in agricultural, farming or forest use, to permit public recreational use, or to forbid or limit any or all:
(...)
This right may be exercised in perpetuity or for a specified number of years. ***It may or may not be stated in the form of a restriction, easement, covenant or condition, in any deed, will or other instrument executed by or on behalf of the owner of the land or in any order of taking.***
http://definitions.uslegal.com/c/conservation-restriction/

Section 31. *A conservation restriction* means a right, either in perpetuity or for a specified number of years, whether or not stated in the form of a restriction, easement, covenant or condition, in any deed, will or other instrument executed by or on behalf of the owner of the land or in any order of taking (...)
*A preservation restriction* means a right, whether or not stated in the form of a restriction, easement, covenant or condition, in any deed, will or other instrument executed by or on behalf of the owner of the land or in any order of taking, (...)
*An agricultural preservation restriction* means a right, whether or not stated in the form of a restriction, easement, covenant or condition, in any deed, will or other instrument executed by or on behalf of the owner of the land appropriate to retaining land or water areas predominately in their agricultural farming or forest use, to forbid or limit any or all (a) construction or placing of buildings except (...)
*A watershed preservation restriction* means a right, whether or not stated in the form of a restriction, easement, covenant or condition, in any deed, will or other instrument executed by or on behalf of the owner of the land appropriate to retaining land (...)
*An affordable housing restriction* means a right, either in perpetuity or for a specified number of years, whether or not stated in the form of a restriction, easement, covenant or condition in any deed, mortgage, will, agreement, or other instrument executed by or on behalf of the owner of the land appropriate to (...)
http://www.malegislature.gov/Laws/GeneralLaws/PartII/TitleI/...

https://www.efanniemae.com/sf/mortgageproducts/pdf/rr.pdf
http://www.lawserver.com/law/state/connecticut/ct-laws/conne...
http://www.ilga.gov/legislation/ilcs/ilcs4.asp?DocName=00650...
http://www.geog.umn.edu/faculty/squires/courses/5361/Lecture...


Per la formulazione in lingua italiana cito l'esempio qui sotto che, seppur estratto da un contesto completamente diverso (si tratta di testamenti biologici), rende bene l'idea:

In particolare negli Stati Uniti, la direttiva di delega (...) costituisce la struttura portante di questi documenti, mentre le dichiarazioni vere e proprie vengono formulate sotto forma di limiti posti dal paziente all’azione del suo delegato”.
http://www.mdc-net.org/it/convegni/seminario-di-studio/134-i...



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Note added at 3 giorni3 ore (2012-11-06 15:49:51 GMT) Post-grading
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Di nulla Stefania, buon proseguimento!