A change to the terms of an LC after it has been authorized is made an amendment. Any time before the LC’s end date, after it has been authorized, an amendment can be made. Under any published ICC rule, there is no limit on how many changes can be made to a letter of credit at this time.
Even so, it might not be smart to change it too often in real life.
There used to be letters of credit that could be revoked.
This type of letter could be cancelled or amended at any time by either the buyer or the bank that sent it, with no need to let anyone know.
This caused a lot of trouble, so the ICC took revocable letters of credit out of the UCP 600 everywhere they were allowed to.
Letters that are irreversible can’t be cancelled, amended, or taken back unless all three parties agree to the terms.