Please use the Question Tags to state the name and full version number of the story format you are using, placing that information within the Question Titile just makes it longer than it needs to be.
The solution to your issues consists of two parts:
1. Marking the text you want to conditionally apply the effect to.
You can use named hooks with with a predetermined name (like blurable) to do this.
2. Conditionally appling the enchantment to the marked text.
You can use the (if:) macro to check the current value of the $alcohol variable each time the Passage is displayed, then use a combination of the (enchant:) macro and the (text-style:) macro to enxhant the known named hook.
Some of the [words]<blurable| in this [sentance]<blurable| will become [blured]<blurable| when \
the value of [alcohol]<blurable| variable becomes large enough.
(if: $alcohol > 5)[
(enchant: ?blurable, (text-style: "blur"))