Pledge of Allegiance vs. Constitution?

[conus00]

I can see where you are coming from in case of The Pledge of Allegiance. From your standpoint and in layman's terms: you are not forced to take it and you or not punished if you do or do not.

But why are the words "under God" included?

Can it be amended so these words are "optional". Like in the Oath of Allegiance (I will have to take to become U.S. citizen)?
"I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I will bear arms on behalf of the United States when required by the law; that I will perform noncombatant service in the Armed Forces of the United States when required by the law; that I will perform work of national importance under civilian direction when required by the law; and that I take this obligation freely without any mental reservation or purpose of evasion; so help me God."

According to wikipedia:
8 C.F.R. 337.1 provides that the phrase "so help me God" is optional and that the words ‘on oath’ can be substituted with ‘and solemnly affirm’.

Why can't the Pledge of Alliance be modified in same fashion?

@SteamWake interesting article. I didn't know all that.