19. Can I opt-in for composition scheme anytime during the year?
No. Before the beginning of every financial year, a registered taxpayer is required to provide a declaration on the GST Portal. This cannot be done anytime during the year.
20. What will happen if I opt out of composition scheme mid-year?
When a dealer opts out of composition scheme all the normal rules are applicable from the day of opting out.
For example, a composition dealer opts out of composition scheme on 15th October 2017. This means that the dealer will have to file two GSTR-4 for the quarters July – September, and October (15 days). The dealer will also have to file GSTR-1, GSTR-2, and GSTR-3 for the period of October 2017 (sales from 15th October until end of the month)
HOW ?
GST SITE-HELP-USERMANUAL-REGISTRATION THEN YOU MAY FIND OUT YOUR REQUIREMENTS.