How to generate code for a referenced model fitable to be merged with the top model code?

Hello,

My final goal is to speed up code generation by generating only the code for modified referenced models and then merge it with the top model code.

In context, I have a top model including many referenced models and subsystems. I already generated code for my top model, and I can find in the files generated files myRefModel2.c and myRefModel2.h. Then I open my referenced model, generate the code for this one and get the two files above. However there contents differ completely for those got by generating top model, and simple copy-past or merging of these files into the top model code is nearly impossible.

Is there a way to configure referenced/top model so that codes can be "interchangeable" ?

Many thanks for your advice.