Corporate actions such as bonuses, rights, extraordinary dividends, mergers/demergers, amalgamation, splits, and consolidations will cause adjustments in the underlying stock's futures and options contracts. 

The basis for every adjustment for corporate actions also must be such that the value of the market participants' positions, on the cum and ex-dates for said corporate action, shall remain the same to the greatest extent possible. 

Depending on the adjustment factor, changes to the base price, option strike values, and market lot will occur. 

In many cases, adjustments will result in a change in the contract's expiry date as well, i.e. the contract will be forced closed before the expiry date and the adjusted contracts will trade instead. 

Depending on the nature of a corporate action, the adjustments would be made to any or all of the above. All open positions would be subject to corporate action adjustments.