Best practice in regards to creating environment specific constants

Question

Hello, we are using Appian 18.4. We have constants that are environment specific; for example, assume we have constant WSDL_FILE. 
 
 - DEV: wsdldevurl.com 
 - QA: wsdlqaurl.com 
 - prod: wsdlprodurl.com 
 Currently, if we refresh data from production into DEV and QA, the constant values are getting updated with the production value. Is there any way we can avoid this? 
 Is it a correct understanding that we can add constants values in the custom.properties file by following this pattern: 
 
 In DEV, the custom.properties file would have a line as constantuuid=wsdldevurl.com 
 In QA, the custom.properties file would have a line as constantuuid=wsdlqaurl.com 
 In production, the custom.properties file would have a line as constantuuid=wsdlprodurl.com 
 
 If this is the case, is there any documentation about this? If not, what are my options?

Mike Schmitt · Answer

> This doesn't help me because when we refresh from production to DEV, for example, the constant value in DEV will be updated with production value. 
 
That's not how environment-specific constants work. If you try this out for yourself, you will find that this functionality has been intentionally set up such that it does not overwrite the constant's current value in the current environment even when importing the constant with a different value from another environment. A better way to think of it is, the exported version doesn't actually carry a value, so that for new imports you need to use the .properties file at least the first time to set it initially.