hi Rajat,
Configure release strategy as below -
Two release codes for X (Say 19) & Y (say 20)
Give authorisation User X - Rel code 19 and User Y - Rel code 20
Configure SES release strategy wherein SES can be either released by 19 or 20 (See Pic 1)
Maintain classification
Now create SES & release with User X having authorisation for rel code 19 only (See Pic 2).
And then try to un-release with User Ywith release code 20, it will not allow & will give error "Not possible to cancel release with code 20" (See Pic 2)
User Y can not un-release with release code 19 as he dont have authorisation for rel code 19.
Try this out in TEST system, hope this will help you.
Reg, Rakesh