You can override every LaTeX inline hook in a config file (see Using LaTeX config files) with
In the new definition, every
#1 is replaced with the respective
text to be formatted. Note that it is unnecessary to enclose the whole
new definition with braces in order to keep re-definitions local. This
is done in the LaTeX source anyway.
Let's assume you wanted to change the appearance of URLs. You prefer the Texinfo way of printing them with a fixed-width font. Then the following line does the trick:
Put this line in the file mymanual-t2l.cfg in the same directory as mymanual.texi. That's it.