Configure HTTP client library with different JSON processing library

Looking at customisation.md it seems that the generator imposes to use specific pairs of http client/json processing libraries.

The pairs are specified as :

• library template (sub-template) to use:
• jersey1 - HTTP client: Jersey client 1.18. JSON processing: Jackson 2.4.2
• jersey2 - HTTP client: Jersey client 2.6
• feign - HTTP client: Netflix Feign 8.1.1. JSON processing: Jackson 2.6.3
• okhttp-gson (default) - HTTP client: OkHttp 2.4.0. JSON processing: Gson 2.3.1
• retrofit - HTTP client: OkHttp 2.4.0. JSON processing: Gson 2.3.1 (Retrofit 1.9.0)
• retrofit2 - HTTP client: OkHttp 2.5.0. JSON processing: Gson 2.4 (Retrofit 2.0.0-beta2)
• google-api-client - HTTP client: google-api-client 1.23.0. JSON processing: Jackson 2.8.9
• rest-assured - HTTP client: rest-assured : 3.1.0. JSON processing: Gson 2.6.1. Only for Java8

However for better integration in our existing applications, we'd prefer the following pair :

HTTP client: OKHttp 3.6.0. JSON processing: Jackson 2.9.7

How would I go about using this ?
Should I craft new mustaches template and code generator by hand which might break in future releases ?
Shouldn't the configuration allow to separately specify the HTTP library and the json processing library ?

Thank you

Start with docs/customization.md and trace the Java client generator's existing library configuration from the documented client templates. Define how HTTP-client and JSON-processing choices would be selected independently, then verify that the generated Java client supports the requested OkHttp and Jackson combination without requiring a separate hand-maintained template.