That's the way to set beneficiaries yes, and when sending @reward.app a memo with 0.001 hive (it sends it back) you just type a number 0-100 which is a % of the author rewards you want to go to curators extra and this will remain that number until you change it with another memo. If you don't send a memo before posting with beneficiary going to it it will use the default 4% going to curators.