Can GM improvise Critical Fumble in PFS?

[GM rainzax]

Hello Community,
As the title.

If I am running a PFS Scenario, can I improvise upon the Tiers of Success mechanic (CF/F/S/CS) to create fun story moments where the outcome of Strikes or others die rolls result in incursion of minor damage or temporary status conditions?

Like falling prone if you roll a "1" to melee strike?
Or a modest 1d4 richochet damage to your adjacent ally if you roll a "1" to ranged strike?
Or, what about if you roll a "20" and splash blood on an adjacent ally to make them momentarily sickened?
Little effects like that.

If the answer is "yes", what are the parameters of this leeway?
If the answer is "no", where is it written that this is expressly forbidden?

Thanks!

[Ferious Thune]

Probably no on the examples you gave. Prone in particular is a big debuff, and I wouldn’t be happy as a player if that got imposed on me outside of the rules. “Flavorful” things, sure, but actual mechanical penalties like taking damage or falling prone, no, because actions that have critical failure conditions say that they have critical failure conditions. Adding them where they don’t exist is a house rule.

[Pirate Rob]

No alteration of mechanics of Player Characters.

Adding extra critical failure/critical success conditions is in clear violation of that.

[GM Numbat]

You can add story elements but not mechanical ones.

You swing with gusto, completely missing your target and barely keeping your balance.

You miss the target, the bullet ricochets off the rock, whizzing past your ally's ear, so close they hear and feel its passage.

You cleave into your foe, splattering all those adjacent with their blood.

Make sure to read your audience and keep it within their comfort levels.

[Blake's Tiger]

Also more explicitly stated in the Table Variation Appendix.

Table Variantion Appendix

Table Variation (bold emphasis mine) wrote:

As a Pathfinder Society GM, you have the right and responsibility to make whatever judgments, within the rules, that you feel are necessary at your table to ensure everyone has a fair and fun experience. This does not mean you can contradict rules or restrictions outlined in this document, a published Pathfinder source, errata document, or official FAQ on paizo.com.

House ruling critical results--fail or success--beyond that described in the source text is a contradiction of the rule.

Table Variation Appendix (bold emphasis mine) wrote:

Whatever changes you make as GM must remain true to the fundamental mechanical structure and challenge of the encounter.

Furthermore, Paizo has officially published critical hit and critical fumble decks, and neither of those is legal in PFS. If the official product version of what you propose is not legal, house ruling it wouldn't be either.

[Sah]

GM rainzax wrote:

Or a modest 1d4 richochet damage to your adjacent ally if you roll a "1" to ranged strike?
Or, what about if you roll a "20" and splash blood on an adjacent ally to make them momentarily sickened?

Besides it not being allowed these 2 confuse me, even if it was allowed. I've played in plenty of games that have allowed them but

The first one is Character X failed, so Character Y gets punished?

The second is Character X succeeded, so Character Y gets punished again?

I guess I am just curious about the rationale behind these ideas.