You can administer the values of your Custom Fields right inside your Shopify account. This functionality is only available when using Google's Chrome browser.
If you haven't done so already, you'll need to install the Custom Fields app from the app store first. Once you've activated the app, you'll be able to use this browser extension.
1.) To get started, install the browser plugin from here. Click the Add to Chrome button. Then click Add Extension.
2.) In your Shopify Admin, Click on Apps on the left sidebar below Discounts (it looks like a Tetris block).
3.) Click on the "Custom Fields" App. By clicking on the app link, the app will silently log you in and take you to the Custom Fields administration area. You can close this new browser tab once the page loads.
4.) Visit a Product in your Shopify Admin. The plugin will show at the bottom of the edit screen. Click on "Wake Up" to load your fields for editing. The app will time-out after a few minutes of inactivity.
5.) That's it! You can now use the plugin to edit your fields in your Shopify store. When making changes, don't forget to click the save button at the bottom of the plugin in order to save your changes in the Custom Fields app.
If you've followed the instructions above and can't get the app to appear in Shopify, check your Chrome settings and make sure you "Accept 3rd Party Cookies". To fix this, open Chrome preferences click on Settings, then Show Advanced Settings. Under Privacy, click on Content Settings.
Make sure "Block third-party cookies and site data" is not checked.