Oolite Bulletins

how to make sub entities affect the status of the ship by example when an engine subentity is blown off it would decrease ship's speed and manheuvering??'

I believe that max speed and pitch/roll are read-only elements of shipdata and cannot be changed via script.

As Ramirez writes, you can't modify much. Only a few characteristics can be modified by removing equipment. e.g. removing the fuel injectors. Or you can lower the 'thrust' to simulate less engine power.
Best example with blown-off subentities is my modification of Griffs krait that can be downloaded through my sign below.