Translate-anything module: I need the full HTML of a page, can I hook in without hacking the theme?

I'm creating a module which will allow admins to enter multilingual text in any text field or text area (in menu's, nodes, blocks, anywhere basically) which will then be passed to the t() function for translation. The module will be even more flexible by also allowing other PHP functions, so it should recognize the functions which are allowed, such as t('string') without being surrounded by <?= ?> per or <?php, perhaps through an alternative syntax like [ff|t('string')]

For example, if the admin has specified that the authenticated users role may use the "t" function, then [tt|t('English text',param2)] would result in t('English text',param2) being parsed as PHP when the page is rendered, To accomplish this I need to hook in somewhere before the HTML is displayed to the user so I can replace all instances of [tt|PHP_function_here()] with the output of that function.

Could anyone advise on how to do this without hacking the template?