1.- the has_knowledge_been_checked calls prompt_for_knowledge_backfill function.
2.- The prompt_for_knowledge_backfill function is stored in cst_fldrtree.js in script folder.
3.- The prompt_for_knowledge_backfill function calls the create_new_ticket function.
4.- in the function create_new_ticket you can preset the category.
Another solution is in detail_cr.htmpl add the following lines
<PDM_SET args.category="pcat:***">
<PDM_SET args.category.sym="category.ss_sym">
Regards
Francisco