I would like to disable at least one of the available search methods, Similar Phrase, for example.
Customer Portal, Answer List Page
To remove an item from the Search By menu, you must edit the report for the end-user page to remove the run-time selectable filter from the report.
Within Customer Portal pages, use the SearchTypeList widget.
This widget defines options listed in the Search Type field when using an answer or incident report. The options in the menu correspond to runtime filters in the report. For answers, the search_nl, search_fnl, search_cpx, and search_ex filters are used to display the Phrases, Similar Phrases, Complex Expression and Exact Search options. For incidents, the search_thread and ref_no filters display as Summary/Thread and Reference # in the menu. If 'search_type_only' is set to false, all runtime filters of type integer (INT) or text (VARCHAR) are also included in the Search Type menu, including both standard and custom fields.
For addtional information, refer to the 'Edit the Search Results Page' section in the online documentation for the version your site is currently running. To access Oracle Service Cloud manuals and documentation online, refer to the Documentation for Oracle Service Cloud Products.