altering tex output of derivatives?



I am working on deriving a partial differential equation for a physical 
model. The expression is long and has partial derivatives of all sorts 
of things, typesetting it by hand is a pain. I've used "texput" to 
describe the tex output for all the various variables, but I want a 
different format for derivatives. Specifically I want diff(a,b,1) to be 
typeset as "\del{a}{b}" which is a macro defined in my LaTeX file that 
automatically sets up a partial derivative for the two variables.

I tried using texput to change the output of diff but it doesn't work:

texconvdiff(arg) := block([a,b,c],[a,b,c]: args(arg), 
concat("\\del{",tex1(a),"}{",tex1(b),"}"));

texput(diff,texconvdiff);

tex('diff(a,b)); <<<<< doesn't output modified derivative
			notation***************

Instead I've set up a pattern rule to replace diff(a,b,1) with del(a,b) 
and diff(a,b,2) with delsq(a,b) and then set the texput for those 
functions, but I wonder why it is not possible to change the way that 
maxima outputs derivatives?