Can a governor amend a bill before signing?

Answer 1

Not in the United States. That would be an Ex Post Facto law and it is forbidden by Article 1, Section 9, Clause 3 of the US Constitution.

However that only applies to criminal law, not tax law, for example there are tax rules for cryptocurrency and the AIG rules (The House of Representative's 2009 vote to impose a retroactive 90 percent tax on bonuses awarded to employees of American International Group) which are retro active (famous Bitcoin etc cryptocurrencies), in addition there are cases of the securities law.

It is known as Ex Post Facto Law. An ex post facto law ( "from after the action" or "after the facts") is a law that retroactively changes the legal consequences (or status) of actions that were committed, or relationships that existed, before the enactment of the law.

A law may have an ex post facto effect without being technically ex post facto. For example, when a law repeals a previous law, the repealed legislation is no longer applicable to situations to which it previously was, even if such situations arose before the law was repealed.In criminal law its controversial and usually prohibited by the constitution but a law can retroactive change a law when it alters the penalty in a positive way, say for example cancels an immediate death penalty or in the family law retroactive allows a same sex marriage which would have been prohibited before.

Answer 2

Yes, but if the president refuses to sign it and sends it back to Congress, a 2/3 vote in both houses of Congress is needed to make it law. If the president just ignores it, a bill becomes law in 10 days if Congress stays in session during those 10 days. If Congress happens to adjourn in those ten days, the bill dies without becoming law, unless the President signs it.

Answer 3

No, the President has no role at all in the case of proposing/ratifying an amendment.

Answer 4

no, the president of a democratic country cannot pass a bill which the congress has not signed

Answer 5

No.