Quick question about non-competes

Looked through the board and didn’t see this specific thing:

I know non-competes are usually unenforceable unless a few conditions are met, one being that you are compensated for it. I read on another post here that if you sign a pledge as a condition of employment at the outset (not at leaving), they can treat your salary as compensation for that non-compete.

Question: what if the pledge comes *during* employment? For example, I was given mine a year after starting and signed it. Could they count salary after that as compensation?

I do not currently have any issues with this clause, I am simply asking out of curiosity.

Also, bonus question: is a non-compete enforceable if it is listed in the company rules (就業規則) and not a specific pledge?

Thanks!