If a URL on your site changes, it is always wise to leave a redirect to the new page. This will help your visitors and search engines. If you create redirects, it doesn't matter too much if you still have a link to the old address in one of your posts. There will probably be a plugin for this, but I don't know which one.
If you really want to keep all links pointing to the latest version, you could replace them with shortcodes that are evaluated to the real URL. <a href="[linkto postid=123]">
would then result in <a href="/2010/08/05/some-post">
. I think this is doable, but I don't know whether a plugin already exists for this.
You can also use this technique to replace short snippets, like your company name. The Shortcode API is really easy:
// [company_name]
function replace_company_name($atts) {
return "My Awesome Company";
}
add_shortcode('company_name', 'replace_company_name');
// More generic
// [replace r='company_name']
// [replace r='company_motto']
function do_replacement($atts) {
$replacements = array(
'company_name' => 'My Awesome Company',
'company_motto' => 'A Company so Awesome even you would want to work here!',
);
return $replacements[$atts['r']];
}
add_shortcode('replace', 'do_replacement');
You can hardcode the strings in your plugin code, or you could create a Wordpress options page where users can add and edit new shortcodes.