1. In the normal course the DC should not accept the petition seeking amendment for covering up the lacuna, however s per law, the DC can allow the petition seeking amendment at this stage if he is convinced by the arguments presented by the concerned party.
2. You can file any petition expressing your strong objections to it.
3. In your argument over the petition he filed you can strongly record your objection in view of the information obtained through RTI act.
4. The court will issue notice to you when he files a petition for this purpose.
5. Yes, or else the court may decide in your absence against you