Tag Page Show Full Content

@skynet: Yes will need to replace the the_excerpt() with the_content(). You should do this change in tag.php file.

Let me know if this resolves your issues!

Regards,
Skandha

@skynet: You will need to create a child theme and customize the site for tags pages to display full content. If you would like to display full content on blog page, tags and archive pages you can enable it from the customizer. I suggest you to create a child theme rather than editing the parent theme directly. Let me know if you need assistance for child theme customization.

Regards,
Tikaram

@skynet: You need to create child theme. There is no doubt on this. After you create child theme, you can copy content.php file to your child theme. Then add the following code after </div><!-- .entry-summary --> in line no 67

<?php elseif ( is_tag() ) : ?>	
	<div class="entry-content">
		<?php
        if ( empty( $options['more_tag_accessible'] ) ) {
	    	$more_tag_text = $options['more_tag_text'];

	    	the_content( $more_tag_text );
	    }
	    else {
			$more_tag_text = $options['more_tag_text_accessible'];
			$more_tag_icon = $options['more_tag_icon_accessible'];

	    	the_content(
                sprintf(
                   $more_tag_text,
                    '<span class="screen-reader-text">  '. get_the_title() .'</span>'
                ).
                '<span class="meta-nav">' . $more_tag_icon . '</span>'
            );
	    }
	    ?>
		<?php wp_link_pages( array(
            'before'		=> '<div class="page-link"><span class="pages">' . __( 'Pages:', 'catch-box-pro' ) . '</span>',
            'after'			=> '</div>',
            'link_before' 	=> '<span>',
            'link_after'   	=> '</span>',
        ) );
        ?>
	</div><!-- .entry-content -->