Hi.... The answer is 'yes' and 'no'.
Yes, because most of our behaviours are learnt and not innate. So if we are in a desperate situation we will find a way to learn new behaviours or unlearn the old ones.
No, because there is no point in trying to change something that comes natural to us. The question is why you wish to change being a soft person who can't be stubborn.
I would suggest you to just learn to be tough with people and situations when they require you to without changing your original nature. It is possible and lot of people doing rough jobs, do that on a daily basis.
Next Steps
Consult a Psychologist.
Interpersonal Guidance and Counselling is required.
Health Tips
Mr. Gunjan Maithil
Senior Psychologist
Cell: nine six seven one three zero three one three four
Website: https://gunjanmaithil.wixsite.com/therapy
App: http://wix.to/fECHB08?ref=cl