Any change to the structure of player inventories would have ramifications for the game's client, the server, and any player data in the database
You can get some pretty sweet, limited edition skins, though - for example, if you bought the 'Warhammer Bundle' during the October 2023 Warhammer 40k Secret Lair, you got two codes, each good for ten premium card sleeves showing the 40k-ified versions of classic cards: Merciless Executioner as "Ork Kommando" Aggravated Assault Krenko, Tin Street Kingpin as "Makari the Lucky Grot" Zurgo Helmsmasher as "Ghazghkull, Prophet of the Waaagh!" Blind Obedience Danitha Capashen, Paragon as "Neave Blacktalon" Najeela, the Blade-Blossom as "Archaeon the Everchosen" Scourge of the Throne as "Stardrake" Beware, though - this is often the priciest way to find new codes
PSA 10 grades can increase value by 200-400% for high-demand Gyarados variants
My educated guess would be they were also opened from these Theme Decks and it all blended together in their memory