Unregistered release deed is in admissible in evidence 

2) mutation of property would not be done on unregistered release deed as it does not confer title to property 

registration has to be done within maximum 8 months of execution of release deed 

it cannot be done after 17 years 

Court has powers to impound document if it is insufficiently stamped 

You cannot change khata of property by using unregistered release deed as it has no value without registration.

The release deed though unregistered is valid in eyes of law  but you cannot change khata. 

See you need to apply before the municipal/revenue authority along the deed for mutation in your favor. Further since the deed is not registered the authority may deny. 

See the document need to be registered and also based on document you can file a suit.

You need to register it. Unregistered deed is bad in law and void

Unregistered release deed is not valid.

Sec 33 ? which act ?

Unregistered release deed will not confer title to you to the share of property that was transferred to you vide the said deed, hence you may not be able to transfer the khata by this deed, you may have to ask that cosharer to execute a registered gift deed once again.

What do you mean by impounding this document?

You are having the document in your possession then why do you want to impound it?

In my opinion you are too confused by imagining lot of things in this regard, you cannot get the title to the share of the property by an unregistered release deed, hence you may do things to make that document a legally valid one instead of imagining some other unrelated things.