Nah, Pokémon Go still doesn’t have a mass convert button for its Rare Candy. There is a trick for speeding up the process, though.
Reddit user sirpaul589 posted a GIF to the Pokémon Go subreddit to demonstrate the process. Here’s what to do: When you’ve amassed a ton of Rare Candy and want to cash in on a specific Pokémon, position the “Yes” button—which pops up when you click on a Pokémon—to line up with the Pokémon you want to use the candies on.
By repeatedly spamming between the “Yes” button and the Pokémon, Rare Candy is converted to specific Pokémon candy quickly. Of course, it’s not as quick as it would be if there was a mass convert button.
Rare Candy Pokémon Go is a special candy that’s usable on any Pokémon in the game, and like regular Pokémon-specific candies, they power-up and evolve Pokémon. Rare Candy is especially handy for boosting rare Pokémon that players might not see too much—and therefore, not earn many candies for. Each Rare Candy must be converted to a specific Pokémon candy before using, however. And if you’ve got a lot, it can take a while to complete the process. The process should speed up with this hack, however.