Any disabled person here with experience of interview and medical in UPSC before?

Sir/Madam, I have a query. I am cse aspirant and will probably appear next year. Last year due to one accident I suffered major knee injury and operations of it including injuries and complications in spine. As a result I got some defects in musculoskeletal system and got certified with 40%+ permanent locomotor disability by CMO headed board of my city after thorough assessment. While going through the eligibility of services I found I am fit for some and unfit for many services if I apply with disability. Post interview when upsc conduct medical exam the reassessment of disability is also done. My questions are following:

1. What if newly evaluated percentage slides down below 40% due to diff in opinion? Will my candidature be cancelled ? Or will I be considered in Open category? What happens when reassessment is below 40%? Do they give final selection or not, given I qualify?  In any case do they raise objection on original percentage of disability certificate?

2. What happens in reassessment? Same medical tests again? Or going through reports? Or physical tests only like push pull fit sit etc? Asking so that I don't suffer fate of Ira singhal madam. 

3. As I am already unfit for many services should I apply in open category only? Will it be feasible? 

Please someone with experience reply.