Attachment.php 3.6: Modifying filedata

[XTF]

Hi,

In 3.5 it was easy to modify the attachment by altering $attachmentinfo['filedata'].
However, in 3.6, that appears to be no longer possible.
Also, in the first query, the first 2 mb are fetched but it seems those same 2 mb are refetched again just before they're send to the client. Why is this?

And is there another easy way to modify the data just before it's send?