Did you know you can buy the tags online? and with some electrical know-how you can make them say what you want. A little time and effort and now you have a tag that says whatever price you want on it. If they got switched at the store at that point, well, how would you know? Just work in teams to make the switch less obvious on the cameras.
I thought the video was going to be about making fake barcodes, for example, photocopy the barcode of the cheap item, print it to a sticker, put the sticker on the expensive item of the same weight, enjoy discount, or be about generating unauthorized clearance barcodes, but going to the grocery store and changing them all to say cool things like crakkka down, ACAB, America Delenda Est, etc. is cool too.
Someone did that something like that once when I worked at a best buy. Someone returned a cheap go pro in an expensive go pro's box. Then I accidentally sold it to someone else, who was irate when they came back.