Hi Kaylyn! There's nothing specifically as far as handlebars goes to insert a random unique code into a template, but in terms of ideas for possible workarounds:
-- you could add these as profile fields to users. Perhaps you could merge this spreadsheet with a list of the user emails you want these to apply to. Then, these would be unique for each user and can be pulled into the template from a profile as normal

--you could also explore having these unique codes be in a data feed, where perhaps you're passing a unique user id to the data feed, and it returns a unique code

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