Question on disposition vs Riven stats

I know that the disposition of a weapon is measured by the weapon's usage popularity (player base). However, my question is:

Is disposition also changing when the popularity of a weapon increases or decreases over time?

If so, would it affect the unveiled or veiled stats of the Riven mod (or in order words, does it affect the existing Riven mod or only when you re-roll the mod)? How often do they (DE) decide to adjust the existing disposition of a weapon?

Thank you.