NL had sanctions in place to prevent stealing other people's patterns. Every QR code is embedded with a player and town ID. If these aren't yours, you can't edit or display them. I fear this may be the case for imported designs in New Horizons. Since They are two different games, your New Leaf QR codes won't be owned by the NH player, unless Nintendo removes these restrictions
In the direct, the player had the options to wear or display a pattern imported from New Leaf. Not sure about editing. We shall see.