Instead of creating a thread, use
https://cracked.sh/usercp.php?action=drafts_templates just like you would for a thread (fill in subject and post body). For my account leak threads I use [bracketed text] as placeholders for the fields that get updated. Then when you create a thread, select "Load Draft Template" on the right side of the subject line to pick which template you want.
If you have an existing thread you want to template, you can go to full edit on that post and use source mode to copy that into a template.