I want to change title/description or add more variations during sales event


You are free to make any changes during sales event. Please go ahead and modify your listings. The only important thing is that sales event discount value must be applied to new price (including variations prices). In this way we can automatically calculate right price for newly added or changed variations after sales event is over so you won't need to modify it manually. 

Related articles

I like the Sales Events Tool! Especially how it put the sale price at the top of the listing and how it calculates the percentages and shows the "sale" and "was" prices!