I wrote a previous post about using props in your yoga practice. Modifications are also there to help us. Due to everyone being completely individual, modifying poses (safely) can help you to achieve the pose that is right for you.
Generic textbook photos are not my friend. Bone structure, body proportions and conditions/injuries are not catered for. While the yoga teacher is there to ensure that you adopt the poses safely, ultimately you are the one that knows your body the most.
If a modification helps you to get into a pose or hold it for longer, then embrace it! Bending your knees in Adho Mukha Savasana (downward-facing dog) or replacing Chaturanga Dandasana (four-limbed staff pose) with your knees on the floor makes your yoga practice more beneficial for you. And at the end of the day, that is what matters. Your yoga practice. Do whatever you need to do and congratulate yourself on doing it!
(And if you do have something unusual, like a long snout, then use it to your advantage)
