... the Sorrowful mysteries are to be your focus for all the days of Septuagesima and Lent.
As correct as this might sound, it is not necessary (although laudable). The six days of the week are to remain as normal (M, TH, Joyous - TUE, FRI, Sorrowful - WED, SAT, Glorious), with Sunday seeing the use of the Sorrowful once again. Normally, the Sunday alone is dictated by the liturgical season, not every single day of the season (i.e., during Easter, the Sorrowful mysteries are not just left out).
The Passion is to be our focus during this holy season of penance, but not necessarily our only focus, especially when praying the Rosary, which rightly includes all of the mysteries of Our Lord's life, upon which we ought to meditate all the year through.
If I were going to do the Sorrowful M's every day, I would do them in addition to whatever is the normal practice for that day, if necessary.