Hi Gabriel,
Just to be clear: you’ve added some custom attendee meta fields and wish to ‘back-fill’ data into tickets that have already been created?
If so, I’m afraid that isn’t directly supported however it would certainly be possible to do this if you feel confident working directly with the database.
The way this data is stored is as a serialized associative array in the post meta table. Each ticket with attendee data basically has a matching post meta entry using the _tribe_tickets_meta meta key – and the data can be found in the meta value field.
Since it is serialized PHP data, it may therefore be easier for you to do this from a PHP script.
I hope that provides some insights!