Monastic Rules Development in China

I have read from the books and articles that monastic rules (vinaya) in China have experienced a few stages of development. Vinayas had changed a few times in China, some Buddhist masters put additional rules or altered the Vinayas.

As we know that Theravada Vinayas are fixed in number and they did not change from the Buddha's time.

Any comments whether the monastic rules can be changed or should not be changed?

with metta,

Vinaya used in China

When we go along the history of Buddhism, the first episode of different views in Vinaya was stated when Venerable Ananda informed the first council about the Buddha's statement: " if the sangha so desire, the sangha may do away with the lesser and minor rules after the lapse of me". But this was turned down by the first council chaired by Venerable Mahakassapa. Nothing will be change in the Vinaya was adopted by the council and this carried down by Theravada up to today. At about the same time,the episode of elder Purana about the disagreement of the first council where he mentioned that he will have his own set of Buddha's teachings and the Vinaya was preserved by Mahisasakas. The Vinayas present today in Chinese were brought down from the era of Nikaya Buddhism. 5 Vinayas are used in Chinese Buddhism today, they are
1. The Ssu-fen lu of the Dharmaguptaka School
2. The Shih -sung lu of the Sarvativadin School
3. The Wu-fen lu Of the Mahisasaka School
4. The Mo-ho-seng-chi lu of the Mahasanghika School
5. The Ken-pen Shou-i-chieh-yu-pu lu of the Mulasarvastivadin School

With the history of Venerable Ananda about minor rules and the spirit of Mahayana Buddhism in China, a lot of adaptation had been made to foster the growth and penetration of Buddhism in all folks of live in China. New rules had to set to suit the new monastic life in China and a lot of cultural differences had to left behind from the original country. Especially Ch'an school in China had developed a totally new rules to follow by the order under this school. However, they didn't change the Vinaya they used but they set the rules parallel with the Vinaya and use at the same time.