A treaty T is signed by two state actors A1 and A2.
Both sides agree to put in place a single customs territory (described herein) for an interim period of two years (described herein).
Both sides will use best endeavours, in good faith, abiding by their respective legal orders, to negotiate the agreements referred to in declaration D.
Declaration D (another document) says:
Both sides have agreed this declaration. This declaration accompanies T, that has been endorsed by A1 and A2, subject to ratification.
This declaration establishes the parameters for future economic cooperation between A1 and A2, to take effect immediately after the interim period defined in T.
For the period beginning immediately after the interim period defined in T, both sides agree to develop an economic partnership that builds on the single customs area defined in T.
Are the agreements within D legally binding in international law? In other words, does the positioning of provisions in a separate document, linked with the "good faith" article, change things?
If the answer is no, if a new executive government is elected within A1 on a platform that differs from D, by what legal mechanism could the agreements in D be reneged on?
The heart of my question is this: does the positioning of provisions in a separate document, linked with the "good faith" article, change the legally binding nature of the contents of the other document?
I realise that a country can simply walk away from a treaty obligation, but I am assuming that both states operate within the rules-based order as far as possible.