You can do it in Rails, something like
group=Group.find_by_name('mygroup')
group_users=GroupUser.where(group_id: group.id)
group_users.each do |gu|
u = User.find(gu.user_id)
op=UserOption.where(user_id: u.id)
op.email_digests = true
op.digest_after_minutes = ???
op.save
end
The above code was generated by a human, who may have been hallucinating. Use at your own risk.