What could be the possible ways when Odoo 9 in production?

For Example, Currently I have modified code from one of module as it is based on odoo 8. And tomorrow Odoo 9 is in production wt that time what i can do with my customized module ?

will it work in odoo 9 as well ?

what will be the way to work my customized module in odoo 9 ?

Please provide paragon information for this.