Changing “amp-helper-functions.php” without losing changes

Hello. I need to make changes in the featured image because they are too small and Google take them as warnings.
And, I use “Multiple Featured Images” plugin, so, I replace that for the featured one. In amp-helper-functions.php I use:

If(kdmfi_has_featured_image('featured-image-2', $post->ID)){
	$imgfb = kdmfi_get_featured_image_src( 'featured-image-2', 'full', $post->ID );
	$post_image_meta = array(
		'@type'  => 'ImageObject',
		'url'    => $imgfb,
		'width'  => '657',
		'height' => '340',
	);
}else{
	$imgfb = "staticURL.jpg";
	$post_image_meta = array(
		'@type'  => 'ImageObject',
		'url'    => $imgfb,
		'width'  => '657',
		'height' => '340',
	);
}

return $post_image_meta;

Is there any way to change this code in another place in my theme_floder\AMP so that I don’t loose it every time amp plugin is updated.