I presume it’s fine to add whatever intentions you want on top of whatever the official intentions are, for any prayer.
The only time I don’t do it is when a devotion specifically says something like “You must pray one rosary for the Holy Souls, or for the unborn, etc. on this day” or something like that, then it would be my personal choice to just do the whole prayer for the Holy Souls, or the unborn etc. and if I wanted to pray for 10 other intentions I would say a second prayer. But that’s my personal choice, it’s not required that a person do it that way.