I've been looking around for a while on how to do this but I don't think I've been wording my searches correctly. I'm developing a custom theme and want to break out a section of a page into a reusable piece that I can reference like you would insert a header with <?php get_header(); ?> but I want to use a different header file instead of header.php. How would I do this?
You can use the function like this:
<?php get_header( $name ); ?>
$name :: (string) (optional) Calls for header-name.php.
if you have a seperate header for home page you can create a header file like this "header-home.php" to call that header file use the get_header function like this:
<?php get_header( 'home' ); ?>
Also you can call multipe header in a theme like this according to different conditions
<?php
if ( is_home() ) :
get_header( 'home' );
elseif ( is_404() ) :
get_header( '404' );
else :
get_header();
endif;
?>
You can specify which header file you want to use by naming it, as Ajith R Nair said in his answer. <?php get_header('new');?> would load the file header-new.php in your theme's directory. If you plan on changing small parts of your header, I suggest not using duplicate header files, but instead define a global variable that holds an array of default parameters in the header file, and just use that same global variable in your theme pages to override defaults. Hopefully that points you in the right direction, though I would be happy to clarify if needed.