Ideally you should stretch after you break a sweat. There is risk of injury when stretching cold muscles. Running about a half mile very slowly then stopping to stretch is ideal. Often ignored but something to think about. Yes, you can change your form.
Natural form is a myth.
Some quirks you may have are ways your body deals with asymmetric differences. They may be necessary, but good form can be learned. For those of you following the basic schedule, forget speed work. If you run and you're normal, your body has a few aches and pains, especially in the morning. Marathoners do a lot of limping and creaking in the morning.