Best Practices: Changing a custom module

Hey guys.

I´m making my first module and I saw these best practices http://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_7.6/API/Application/Module_Builder/Best_Practices_When_Building_Custom_Modules/

But what is the proper way to maintain the module ?

Scenario: Custom module "pizza" is made on TEST. It is has already been deployed in PROD. Lets say I want to add a field to it or something.

Is that done in Studio on the PROD or do should I maintain the module on TEST and then redeploy (which seems to be NOT recommended)?

Probably just maintain in Studio, huh...

Thanks

KGM