The better (I think so), define ContextFile as a context variable with the appropriate value depending on the context (Development, Test, UAT, Production).
For each concerned job, go to the job tab, then Extr, uncheck the option "Use Project Settings", check the option "Implicit tContextLoad", choose "From File", set the "From File" field as "context.ContextFile" and set the "Field Separator" field as "==" (for example).
Finally, define your key/values context files using "==" as a separator.
As @TRF says. I will add that instead of a context variable, the path to the config path can be a system environment variable. And you use System.getenv("some variable name").
This way you know when your config are by querying the environment variable you defined.
Introduction to Talend Open Studio for Data Integration.
Practical steps to developing your data integration strategy.
Create systems and workflow to manage clean data ingestion and data transformation.