Why I can modificate variables in Headincludes Template?

[Jhonnyf]

I try to modifycate $vboptions[keywords] that it's call in headincludes template and I can't.... i use a plugin and this code

PHP Code:

$vbulletin->options['keywords'] ='New keyords'; 


after I put a custom variable as $my_var (headincludes to add more keywords) and I can't change this with a plugin (always show me empty)

I thing that maybe this is precache or something else

Hooks that I try:

forumdisplay_complete
global_complete

Thank You