The phrase "amended only by" is correct and usable in written English.
It can be used in legal or formal contexts to indicate that changes can be made exclusively through a specified process or by certain parties.
Example: "This agreement may be amended only by a written document signed by both parties."
Alternatives: "modified solely by" or "changed exclusively by".
The federal constitution, moreover, could be amended only by a unanimous vote of the states.
If the bylaws can be amended only by a shareholder vote, he said, a shareholder meeting must be called.
Two "entrenched" clauses, on language and franchise, could be amended only by a two-thirds majority vote in Parliament.
The issue centred on the revision and patriation of the British North America Act of 1867, which could be amended only by the British Parliament on Canada's behalf.
Third, as a corollary, constitutions became entrenched written documents expressing a "higher" law, which could be amended only by the people as a whole or by some supermajority that could plausibly be said to represent their will.
But Ireland has quite an extensive written constitution and it can be amended only by process of national referendum.
Tonga's constitution, granted in 1875 by King George Tupou I and amended only slightly since, established a constitutional monarchy.
Carmakers could make amends only by focusing on electric or hydrogen vehicles which emit little more harmful than water and might thus prevent millions of illnesses.
All three main political parties have collaborated with a pressure group that campaigns against press intrusion on a form of regulation that is underpinned by parliamentary authority – their proposed royal charter could only be amended by two-thirds majorities in both houses – which means by politicians.
Once established, the limitation year may be changed only by amending the plan.
The Bush administration could amend the diesel rules only by restarting the time-consuming procedure that produced the new standards.
