[AUCTeX] Customizing "%cS" in TeX-expand-list

[jfbu]

Hi,

I have upgraded to AUCTeX 11.88 via Elpa. Thanks to all who
worked on it, as for the first time since quite a few years
I experience the joy of not having C-c ` open some "TeXLive 20xx"
window or, worse, tell me "Error occured after last TeX file closed"

(the few times I tried an upgrade since 2011, it
made things worse, and I had to revert to an ancient auctex
installation copied-pasted from some other machine).

I was quite elated to see that C-c ` works as expected with 11.88,
(it probably does since a long time, I was just unable to upgrade
earlier)
and there is a very nice Error Overview menu entry which I didn't
know about until now. (or did I just not see it? possible)

Thanks to the experts who made this happen: Mosè, Tassilo, ..., sorry
for the people I do not cite but I subscribe to the mailing list
since only very recently. Great job!

This message is about some customizations which I did some years back,
at a time when I very temporarily to some vague elisp understanding,
and that I am re-integrating to my custom-file (the understanding having
vanished)

My question is about how doing the things more effciently than my
current method, which is to customize the full TeX-expand-list variable
for only one change.  

The
default definition of %cS as found in TeX-expand-list is

("%cS" TeX-source-specials-view-expand-client)

I replace it by
("%cS" (lambda nil "/Applications/Emacs.app/Contents/MacOS/bin/emacsclient --no-wait 
+%%l %%f"))

This is to avoid having to put an alias to emacsclient in /usr/bin (which would 
quite possibly be wiped away by system upgrades) or more generally in $PATH

Also this spares me having to put an editor entry in .xdvirc

(I also configured the program for output-dvi to be, in case source-specials is 
on:

open -a XQuartz && %(o?)xdvi -sourceposition \"%n %b\" -editor \"%cS\" [some 
paper option] %d

and for output-pdf:

/Applications/Skim.app/Contents/SharedSupport/displayline -b %n %o %b

This is all on Mac OS X, and my Emacs is recently upgraded "Emacs Mac Port":
GNU Emacs 24.4.3  from https://github.com/railwaycat/emacs-mac-port
)

What I do currently is to have the full TeX-expand-list
customized in order to apply this single replacement of "%cS"

Is there a Lisp-way to do this more economically?
Could I just overwrite the TeX-source-specials-view-expand-client function?

A second question:

I know AUCTeX has many many features, and I am only using a small
fraction. Currently I observe that the first loading when I launch
Emacs and open a first .tex file takes noticeable time (about five seconds).

Is there a "mode-for-the-dumb-guy-who-thinks-he-needs-only-a-few-things" which 
would load faster?

(my set-up: mac os x Mavericks,
Emacs Mac Port 24.4.3, with AUCTeX 11.88 as installed via ELPA.)

best,

Jean-Francois