Need help with Nagios scripting

hye,

I) so am using nagios through centreon. i now understand were perl plugins should be written "in libexec" but my question is , i just create a file via VI write the script in it , and use it through centreon interface?

II) lets say i would like to add a drop down menu to this webpage "please find below image"

where do i implement the code for the new tab,in which directory? and when the new tab is implemented via php ,should i create a perl directive to it?

Thanks