Destiny is a big force so it is difficult to change the destiny but not impossible. Destiny can be changed by the native himself or by the writer of his destiny i.e. God or by someone like a Siddha Yogi having special blessings of God.
Destiny exerts a very strong influence on every aspect and weather of life whether it is spiritual or materialistic. But it should not be forgotten that man is free to make efforts and to perform auspicious or inauspicious Karma (deeds). If one follows one's conscience with strenuous mental discipline and walks on the path of truth then he certainly succeeds in expiating his bad Karmas and eventually lot of good Karmas get added in his destiny.
The Sanskaras of one's previous births make the native have faith in God. One's faith in God encourages him to do prayer. Regular practice of Prayer proves instrumental to control the thought process thereby destroying all evil thoughts. Purified thought process develops thinking power thereby bringing refinement in one's thoughts. Refined thoughts help you follow the practice of Bramhacharya (To stay away from sexuality and greed) and with the power of Bramhcharya also we can do wonders in our life.
Therefore people in all walks of life in Indian society believe in observing Bramhacharya Vrata (Fast). All great Seers, Rishies, Yogies, Saints, Sages and Prophets advocated the importance of it. M.K Gandhi has also given special commentaries on it. With the power of it one can change other's destiny also. He can become competent enough to change the character of the age in which he lives. How successful he will be in achieving the desired results shall depend on the fact that how much mental discipline on which level is observed while practicing Bramhacharya. Therefore the efforts made to have self-control can be termed as most superior Karmas because one who rules himself can rule all.
Therefore we can say that Karma is as important as important is our destiny. We can conclude that performing remedy is also Karma. According to Buddhism by regular and continuous chanting of sacred Mantra "Nam Myoho Renge Kyo" destiny can be changed but the fundamental fact is that spirituality (leading a holy life) is above all religions and it can help one to bring desired change in destiny. Sexuality and greed are greatest obstacles in one's spiritual progress. Everybody has the potential to enrich himself spiritually; therefore, path of spiritualism must be revived and encouraged.
Guru gives Deeksha to his Shishya (disciple) to make him capable to do Sadhana (spiritual practice). Shishya can succeed in Sadhana only if he works with pin point concentration. With the blessings and guidelines of divine Guru one can make his life disciplined and holy by continuous practicing of Bramhcharya, Bhakti, Dhyan, Hathayoga, Mantrajapa, Kundalini Awakening or systematic and regular practice of Srividyopasna. Guru presses hard on the necessity of bringing purity in food, thoughts and behavior before initiating Shishya on the path of Sadhana.
As per astrology our horoscope contains an account of the auspicious deeds and the sins of our previous lives. On the basis of this notion and Shastrik proclamation we can say that our destiny is dependent on the Karmas of our previous birth. Science also believes it that the result of Karma is certain and that comes to us instantly or later.
According to Newton's third law of motion - To every action there is an equal and opposite reaction. On the basis of these principles we can conclude that a man's destiny shall be as bright as the Punya earned by performing auspicious Karmas similarly the misfortune shall be bad in proportion to the sins committed with one's bad actions of previous life. One has to go through very difficult practice of asceticism and do big remedies to change very bad destiny into a good one, whereas, if the magnitude of Punyakarmas shall be more a little effort in the form of small remedies can help in bringing the desired change in destiny.