Slitherine

Several decisions apply negative or positive regional modifiers, with timers. As and example - the "Gods of Old" decision can apply a positive "Deification Degree" modifier, and a decision to free slaves (Freedmen laws?) can apply a "Furious Slavers" negative modifier.

The problem - if the modifier is already present in a region, getting and activating the same decision again in that time period has no effect on the modifier.
For example - getting and activating the decision that allows to free slaves while having the "Furious Slavers" modifier still in effect from a previous one means I can enjoy the benefit of the decision (turning slave pops into non-slaves) without suffering the downside. The already existing "Furious Slavers" regional effect is unchanged - including the shortened timer from the turn when it was first applied.
On the other side, the effects of positive decisions (like "Gods of Old") are wasted, since the timers on the pre-existing modifiers are not reset.

So the suggestion is, when applying an already existing Decision effect with a timer - reset the timer to the original period as defined by the decision.

This makes sense. I'll see if a generic solution to this problem can be added without too much troubles.

Splitting the slave decision so you can actually sell slaves when you need gold and not have the 500 gold needed to activate it.

That's the limits of the decision system here indeed, the conditions apply to all choices ...