The only way I can think of to do this currently is to create, say, 200 statuses. 100 for -Int/+Finesse and 100 for +Int/-Finesse. Make sure to delete the icons associated with these stats and potion effects.
Then lookup the characters Finesse and Int when the status is applied and determine which is greater and the difference and apply the appropriate status.
When the main status (the one the ability you are making applies) wears off, remove these as well. Make sure you store the name of the hidden status you applied so you don't need to figure it out again.
If this skill is ever used in a context where it's possible to get a differential of 100+ stats, you either need to make more statuses or put in the skill "This ability will only swap, at most, 100 points".
I'm not joking : (
Last edited by Sinistralis; 08/10/17 11:59 PM.