Use the 'gu_fix_repo_slug' filter to change the default wp-content folder name.

change-default-content-folder.php

<?php
/**
 * Usage of 'gu_fix_repo_slug' filter.
 *
 * @package wordpress-plugin
 * @link https://github.com/afragen/git-updater/issues/971
 */

/**
 * Plugin Name:       Change Default Content Folder
 * Plugin URI:        https://gist.github.com/afragen/9dafb92dc89fac663b9c2cc3a66d8eba
 * Description:       Use the 'gu_fix_repo_slug' filter to change the default wp-content folder name.
 * Version:           0.2
 * Author:            Andy Fragen
 * License:           MIT
 * Requires at least: 5.2
 * Requires PHP:      7.0
 * Gist Plugin URI:   https://gist.github.com/afragen/9dafb92dc89fac663b9c2cc3a66d8eba
 */

add_filter(
	'gu_fix_repo_slug',
	function ( $plugin_data ) {
		foreach ( $plugin_data as $key => $value ) {
			if ( is_array( $plugin_data[ $key ] ) ) {
				foreach ( $plugin_data[ $key ] as $key2 => $val2 ) {
					$plugin_data[ $key ][ $key2 ] = gu_update_string( $val2, 'wp-content', 'content' );
				}
			} else {
				$plugin_data[ $key ] = gu_update_string( $value, 'wp-content', 'content' );
			}
		}
		return $plugin_data;
	},
	10,
	1
);

/**
 * Update string.
 *
 * @param string $value Value of string.
 * @param string $old   Value of old string to element.
 * @param string $new   Value of new string element.
 *
 * @return string
 */
function gu_update_string( $value, $old, $new ) {
	if ( strpos( $value, $old ) ) {
		$value = str_replace( $old, $new, $value );
	}
	return $value;
}