Can I use coconut oil to soften crust in nose?

It is always best to speak to your surgeon since septal perforation repairs can be complicated and different methods may have been utilized by him. In general it is often a good idea to keep the now moist and lubricated. Sounds like you are doing this. There is a nasal saline gel that can also help to soften scabs in addition to the nasal saline. Again ask your surgeon if this is ok to use. 

Healing after repair of a septal perforation can be tricky. I would recommend speaking with your surgeon before manipulating or using anything in your nose. I often will have my patients use bacitracin or mupirocin     Good luck

Often mild moisturizers like aquaphor can help. But you are best to ask your surgeon. Good luck......