Nope no nested blocks.
The one who has changed the block used the command "add attributes" which is provided by AE. (look at doc attached)
This attribute becomes part of the block, you can put it anywhere, name it like you want, manipulate it like it was part of the block, even set it invisible but like you can see it is gone if you explode it.
Best way is to follow advice of Pat and make new block with appropriate attributes.
Peter