Removing limits on character numbers in a certain post or thread/for a certain person

[MTGDarkness]

I have the issue at my site that a few posts need to be really, really big. Like, massive. And I really don't want anyone to be able to make non-approved posts that size-just me and one or two of my mods.
I've been trying to work this in to a plugin, but I've had no luck so far.

In postdata_start.

PHP Code:

if ($userid=151)
{
$postmaxchars=0;
} 


PHP Code:

if ($userid=151)
{
$options['postmaxchars']=0;
} 


PHP Code:

if ($userid=151)
{
$vbulletin->options['postmaxchars']=0;
} 


(151 is the uid of the guy who needs to make the 50-page-posts)
It doesn't work. What do I have wrong, and how can I do this right?'