I am going to run a fun one-shot for my party, and I want them to win some "prizes" (A gold ribbon, a silver ribbon, a bronze ribbon) that will change one of their stats. As an example:

STR - Gold ribbon - Set STR to 12, SIlver ribbon - Set STR to 10 , Bronze ribbon  - Set STR to 8

Is it possible to do this so it overrides any attribute pluses they have and just sets the score to that, similar to how belts of <Giant> Strength work?

The idea is they go to a carnival featuring the "Olympics", where they complete in tests of each of their attributes and win "prizes". Of course, these are more like participation trophies than anything else, but once they wear them, they cannot take them off. In the carnival, there will be an adventure in which they will have to deal with their new stats. Hopefully, hilarity ensues.  Once they leave the carnival/have a long rest, they will be able to take the ribbons off.

Another idea might be that they pick out a prize which may increase or decrease their stats, so all of a sudden the wizard is just a beast while the fighter is now a genius...

Quote from Merigold00Yahoo>>

Is it possible to do this so it overrides any attribute pluses they have and just sets the score to that, similar to how belts of <Giant> Strength work?

Yes and no. Yes it’s possible to set it up like how a belt of giant strength works. No, it’s not possible to set it up to override any attribute bonuses they have. The way those belts work, they “set” the score to a certain number, but “the item has no effect on you if your Strength without the belt is equal to or greater than the belt’s score.”

Thanks. I cannot set it to a certain value, but I can decrease by a certain amount, like -2, -4.  I will see if that idea works.

You would need two modifiers on each item, one to zero out the current and then set the new value.

Gold Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 12

Silver Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 10

Bronze Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 8

I don't know how this method might interact with other items that may impact the PC's STR score.

Good thinkin,’ that never would have occurred to me.

Quote from Mairondil >>

You would need two modifiers on each item, one to zero out the current and then set the new value.

Gold Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 12

Silver Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 10

Bronze Ribbon:

MODIFIER TYPE: Bonus 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: -20

MODIFIER TYPE: Set 
MODIFIER SUBTYPE: Strength Score
FIXED VALUE: 8

I don't know how this method might interact with other items that may impact the PC's STR score.

That works!