I worked at a major NYC department store while in college in the late 1970s.
We did the same thing. All the time.
Day before the sale, we’d replace the price signs with higher prices for the items going on sale.
That night, we’d put up the “sale” signs with prices often higher than they had been two days prior.
But since we had had the higher prices displayed for that one day, the “sale” signs that said the reductions were from those higher prices were technically accurate.
What a great place to work!
Ha. I just realized the store I worked at was one of two anchor stores in that smallish mall and the other one was Penny’s.