[Vorbis] Simple OGG editing without re-encoding?

[Marcin Kasperski]

I have some OGG files which would benefit from the following 
simple corrections:

a) removing left channel (which is empty) and changing right 
channel to the mono channel (mono sound stereo-recorded by 
mistake)

b) volume change

Of course I can open the files in audacity and do those 
corrections but that would require re-encoding. And I am afraid 
that it will result in additional loss of the quality.

So I have two questions

1) Is it possible to perform those changes 'in place' - without 
decoding and reencoding? From my naive point of view it seems 
that those changes should not require reencoding but heavy 
googling did not help to find any suggestion how to do this.

2) Is re-encoding to be worried about? In other words: if
    B.ogg = ogg-encode( ogg-decode( A.ogg) )
is the quality of B.ogg worse than the quality of A.ogg?

PS I am on Linux.

PS2 As it is my first email to the vorbis mailing list, I would 
like to make thanks to all the people involved in creation of 
this excellent piece of software.