Good day,
your question has been forwarded to me for answer.
Sadly, this is not a valid modification to the magazine.
The casing itself need to be "permanently" modified.
http://laws-lois.justice.gc.ca/eng/regulations/SOR-98-462/FullText.html
(4) A cartridge magazine described in subsection (1) that has been altered or re-manufactured so that it is not capable of containing more than five or ten cartridges, as the case may be, of the type for which it was originally designed is not a prohibited device as prescribed by that subsection if the modification to the magazine cannot be easily removed and the magazine cannot be easily further altered so that it is so capable of containing more than five or ten cartridges, as the case may be.
(5) For the purposes of subsection (4), altering or re-manufacturing a cartridge magazine includes
(a) the indentation of its casing by forging, casting, swaging or impressing;
(b) in the case of a cartridge magazine with a steel or aluminum casing, the insertion and attachment of a plug, sleeve, rod, pin, flange or similar device, made of steel or aluminum, as the case may be, or of a similar material, to the inner surface of its casing by welding, brazing or any other similar method;
Hope this answer your question.
Regards