Is there is a way to specify the set when pasting cards in the deck editor ?
Unfortunately not, no. Lackey doesn't support any way to specify when pasting, nor does it give me (the plugin maintainer) a way to specify default or preferred printings. It always grabs the latest one, alphabetically, which is why basic lands always get pulled from Zendikar Rising. (It's also why I started prepending numbers before promo/alternate/Secret Lair set codes, to ensure they're listed "before" everything else and are never the default when pasting.)
Ok thanks!