[development] hooks after hook_menu is called, but before page rendered

[_craig]

I'm in the process of updating taxonomy_breadcrumb to work with 5.0 and as
part of the upgrade I'm making a few improvements to the module.  I want
to have an opportunity to change the breadcrumb trail after hook_menu has
been called, but before the page is rendered in the theme.  I'm not able
to find any way to do this.  Any suggestions?

It seems as if I need a hook added right at the end of
menu_execute_active_handler() in menu.inc, after call_user_func_array (but
before returning).  Am I missing something?  How can I have a function in
my module execute after any other hook_menu's have been executed?

In the rare case I'm not overlooking the obvious how to I begin the
process of trying to get a new hook added?

Thanks!
Craig