So I am wrapping up v2.0 of my website, and being the perfectionist that I am, I would like to tweak MySQL, but am unsure of the consequences of this?!

(BTW, the purpose of these questions is to identify any *obvious* issues that I might create. Since you guys can't see my entire code base, I realize my questions below are somewhat vague...)

Proposed Change 1:
I have some Junction Tables which have Composite PK's, and I would like to add an "id" field that is an AutoIncrement and a UK.

This shouldn't affect any table relationship.

And it shouldn't impact any SELECT statements.

Could it impact any INSERT statements that I have in my PHP code? (Or will MySQL take care of the AutoIncrement itself?)

Proposed Change 2:
I have the following table...

id (PK)
article_id (U1)(FK)
member_id (U2)(FK)
subscribed_on (U3)
I would like to flip the PK and UK's.

Will MySQL or any SELECT, UPDATE or INSERT statements, or my PHP care?

As far as I can see, this should only impact my Foreign Key Constraints....