Yes, just make sure that they’re aware of your working and they are okay with it. Casting spells on someone else without their permission is not a good idea (personal opinion).
If you are using this Uncrossing spell, while you are burning the incense, send your intention (thoughts, energy) their way. 
You can write a few words or improvise something to direct the energy from the spell to go to them to help with whatever they need help with.
Another way to cast a protection spell on someone would be to create a protection talisman or charge a stone with your intention, and give it to that person.
Good luck!