Marcus Downing

Adds an “Identifier” column to the All Posts and All Pages admin panels, and to any custom post types. 
This column goes just after the Title column and shows each page’s slug, indented if necessary.

Page Identifier Column

Adds an "Identifier" column showing a post of page's slug, just after the Title column.

Scott Reilly

By default, WordPress only allows 30 custom field names/keys to be listed in the dropdown selection ‘Name’ field when writing a post or page. If you, or the plugins you use, make use of a lot of custom field key names, you may surpass the default limit resulting in some custom field keys not being listed. This may force post authors to manually type in custom field key names if they aren’t listed, which increases the chances for naming errors (typos, or not using the precise key name that is needed). This may also cause some authors concern wondering where previously used custom field keys have gone since they aren’t listed.
This plugin increases the limit to 200 custom field key names.
There is no settings page to customize the default value. If you’d like to list some number of custom field key names other than 200 (say, for example, 100), you can do so in either of two ways:
<ol>
<li>By editing your wp-config.php file and at the end adding a line such as: 
define( ‘CUSTOM_FIELD_NAMES_LIMIT’, 100 ); 
-or-</li>
<li>Somewhere — ideally in a mu-plugin or site-specific plugin, or less ideally your active theme’s functions.php file — hook the ‘c2c_list_more_custom_field_names’ filter and return the number you’d like to use: 
add_filter( ‘c2c_list_more_custom_field_names’, function ( $limit ) { return 100; } );</li>
</ol>
Notes: 
* The constant, if defined and truthy, takes precedence over the filter. 
* If either the constant is defined or the filter is hooked but the value configured or returned is not an integer (or an integer string), then the plugin’s default will be used. 
* The limit specified must be equal to or greater than the WordPress default of 30.
Links: <a href="https://coffee2code.com/wp-plugins/list-more-custom-field-names/" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://wordpress.org/plugins/list-more-custom-field-names/" rel="ugc">Plugin Directory Page</a> | <a href="https://github.com/coffee2code/list-more-custom-field-names/" rel="nofollow ugc">GitHub</a> | <a href="https://coffee2code.com" rel="nofollow ugc">Author Homepage</a>

List More Custom Field Names

Allows for more existing custom field names to be listed in the dropdown selection field when writing a post.

Page Identifier Column vs List More Custom Field Names