Can I use dynamic variables when setting up user-defined Slack messages?

Yes, this is possible- however, please use the following variables for ticket description, last public note, and last private note so that only the text content of the description and notes is sent to Slack; otherwise, the HTML tags will get pushed to slack as well.

• Use {{ticket.description_text}} in place of  {{ticket.description}
• Use  {{ticket.latest_public_comment_text}} in place of {{ticket.latest_public_comment}}
• Use {{ticket.latest_private_comment_text}} in place of {{ticket.latest_private_comment}}