Hello Lars,

Very much like you, I am new to the list 
(albeit not entirely new to Inkscape itself).

If Inkscape allows for user scripting, however,
which I am not sure if it does, 

(Edit) I had to google and I found a blog 
post titled "Inkscape extensions by non 
developers, for non developers. A primer". 
The post explains it is possible. 

To avoid breaking the url across lines, 
I decided to shorten it, so see 
non-developers like you and me could
create an extension. It's a bit intimidating 
to think about it, but maybe it could be done
by non-developers, I don't know.)

then an ordinary user could write a script 
(or extension) and make the process 
automatized.

Providing that the part you want to edit is selected,
the extension would need to:
a) create new layer and name it "1st temporary (layer)",
b) move currently selection to the newly created temp layer, 
c) create another layer and name it for example "2nd temp (layer)",
d) reverse the selection,
e) move new selection (i.e. all but those in the 1st temp layer) 
     to the second temp layer,
f) lock and g) hide the 2nd temp layer, 

This way we would be able to select and edit the parts 
from "1st temp layer" only, as you suggested.

Kind Regards,
DyslexicAweTalent

P.S.
To editors of the list. Maybe you want people who 
are new to the list, like me, to read the reminders how 
to contribute to the list, using a numbered list like that
(just a humble proposal):

1) If sending a new submission, send it 
     to inkscape-user@...1648...forge.net

2) If replying, the Subject line should be changed 
     from generic "XXX digest" to a "Re:" and 
     more specific subject.

Date: 30 Jan 2017 15:41
From: "Lars" <noreply@...3267...>
Subject: Edit particular part of SVG only
> Say an SVG file has a chair. The chair is composed of several parts. It
> has a back, legs, etc.
> Can one part be completely isolated?