If the Feds charge someone with a charge on the plea agreement do they go by that charge or will they fix the plea agreement if it has already been signed by defendant prosecuter and judge

If the Feds charge someone with a different charge then what was put in the pre agreement then on the original agreement will they fix it or do they have to go by what is on the plea agreement that was signed by everyone

If I understand what you are saying, they would have to abide by the original agreement. But do you mean that the agreement was signed by the judge before the charges were filed? That doesn't make any sense.