Really nice custom badges you have there!
Since it’s possible to bulk add users to a group, you could then: Grant a badge for all members of a group
Alternatively, if you are comfortable enough with Ruby, you could write and execute a Ruby script in your production environment, along the lines of:
# or you can lookup users by username/email
users = User.find_by(id: [1, 2, 3, ..])
# 100 is the id of the badge
badge = Badge.find(100)
users.find_each { |user| BadgeGranter.grant(badge, user) }
From a long term perspective, I think maintaining and granting badges on a regular basis will do?