Hi,
updating classes on existing modules is challenging especially on Kentico's own core modules.
If possible just recreating it on the second environment might be safest.
That being said, there is a way!
Although talking about custom modules, the steps mentioned in the following blogs might get you started how and why things work:
Summarizing the steps you need to update the ecom module to set it in development mode:
I'd be extra carefull in updating DB's directly!
If you run the following SQL query:
update CMS_Resource set ShowInDevelopment = 1, ResourceIsInDevelopment = 1 where resourcename = 'CMS.Ecommerce'
The module is unsealed and you can export it unsealed. As explained in Jeroen Furst's blog you need to keep the module unsealed during export to include the class definitions.
It's important to unclick the checkbox:
Using this approach I've just expored the cms_class.xml.export of the module that included my custom field.
Again be extra careful on rolling this out, make backups and make sure you test it properly before rollout.