Can extra holes be drilled in a PV module frame to fit mounting hardware?

No. Do not drill extra holes or alter a PV module frame simply to make mounting hardware fit. Canadian Solar’s standard-module manual prohibits additional holes or frame modifications and limits bolted mounting to the existing rear-frame mounting holes. Trina Solar’s Vertex manual also prohibits additional holes and requires approval for alternative installation methods. Check the exact module manual, mounting-system instructions and project drawing before ordering or installation. If the hole pattern or hardware does not match, stop and select compatible parts or obtain a manufacturer-approved mounting solution. Do not treat an improvised hole pattern as an approved connection.

Sources: Canadian Solar, Installation Manual of Standard Solar Modules, pages 13–14: https://www.canadiansolar.com/wp-content/uploads/2020/08/Installation_Manual_of_Standard_Solar_Modules_en.pdf Trina Solar, Vertex Series User Manual, pages 17–18: https://www-cdn.trinasolar.com/wwwstorage/sites/5/UM-M-0002-PP7-Trina-Solar-Vertex-Series-User-Manual_EN.pdf