Actually it states on the site that it was effective November 8. This ends people taking one year back to back diplomashttps://www.canada.ca/en/immigration-refugees-citizenship/news/2024/11/new-international-student-program-regulations-take-effect.html
Effective today, doesn't say change of course but only when changing learning institutions.
https://www.canada.ca/en/immigration-refugees-citizenship/services/study-canada/change-schools.html
Starting November 8, 2024, you must be enrolled in the designated learning institution (DLI) named on your study permit. This means you can no longer change DLIs by letting us know through your online account. To change DLIs, you need to apply for a new study permit.