Amendment of pleadings

Both the parties married under the special marriage act 1954 on 07/01/2013. Wife filed a suit for divorce against husband on 01/12/2017 Section 13 of the Hindu Marriage Act, 1955. Husband sent a legal notice on 07/12/2017 to his wife for restitution. Wife sent reply letter on 02/01/2018. On 23/01/2018 husband appeared before the Family court in the Divorce suit. Husband filed a RCR Case Under Section 22 of the Special Marriage Act 1954 on 05/02/2018. On 06/06/2018 husband filed his WS for Divorce suit. On 16/06/2018 wife filed counter issue for her divorce suit. And on 16/07/2018 wife filed a application Order VI Rule 17 of the Code of Civil Procedure, 1908 for amendment of Hindu Marriage Act 1955 to Special Marriage Act 1954. and changing date of marriage i.e. 06/12/2012 to 07/01/2013 and changing of cause of action i.e. 06/12/2012 to 07/01/2013. My question is (1) Shall Court allow application of amendment of plaint filed by wife? (2) What are the settled principles for amendment of pleadings? (3) Amendment is allowed if it changes the cause of action?