I am sure there are easier ways to do this but this way worked for me. NOTE: I only added "foodCanBeef", to add more be sure to add a comma between names.
<progression>
<set xpath="/progression/perks/perk[@name='perkMasterChef']/effect_group/passive_effect[@tags='foodBaconAndEggs,foodBoiledMeat,foodGrilledMeat,foodBakedPotato,foodCornBread,foodCornOnTheCob,drinkJarRedTea,drinkJarCoffee,drinkJarGoldenRodTea']/@tags">foodBaconAndEggs,foodBoiledMeat,foodGrilledMeat,foodBakedPotato,foodCornBread,foodCornOnTheCob,drinkJarRedTea,drinkJarCoffee,drinkJarGoldenRodTea,foodCanBeef</set>
</progression>
Check the video tutorial for maybe some help on the second part of your question