Injecting code into existing template code

[NathanLedet]

I'm not sure how to do this. I'm not sure if I need to use hooks or if I can do a str_replace (is that even good practice with vB4?).

Basically, I want to write a plugin that injects an image in the header, after the "Welcome, user" text.

The easy thing would be to just modify the template, but I want to avoid modifying any of the core templates.

header template

PHP Code:

<li class="welcomelink">
     {vb:rawphrase welcome_x_link_y, 
     {vb:raw bbuserinfo.username}, 
     {vb:link member, {vb:raw bbuserinfo}}}
//injected code here?
</li>