copygen VS copier

Copygen is a type-based code generator for the Go programming language. Copygen allows developers to generate type-to-type copy functions out-of-the-box without reflection (why?), but it can also be used to generate code. As an example, disgo is a performant, secure, and thread-safe Go Discord API Wrapper that uses Copygen with dasgo to achieve feature completion.

An alternative is to use a reflection based struct copier library or a codegen struct copier library

Disgo is the only Go API Wrapper using a maintainable approach to become feature complete. Disgo is the only Go API Wrapper to provide OAuth2 flows. Disgo is the only wrapper to define API definitions (objects, requests, commands) as structs, allowing for usage of the Discord Producer API without requiring knowledge of an additional API Wrapper Consumer API.

Copygen allows developers to define types, structs, and more in its setup.go file and has no issues copying them to the output; except for comments. The Go AST makes it "very difficult to update the AST and retain correct comment place (from 2017)" and is not likely to change any time soon. As a result, Copygen sometimes generates free-floating comments (i.e multi.go). Copygen's comments are handled in its Parser. Feel free to use any necessary libraries or rewriting of the comment-parsing mechanism to fix this issue.

When the internal model and the API model are pretty much the same, you might simply copy the result from one struct to another using e.g. https://github.com/jinzhu/copier

An alternative is to use a reflection based struct copier library or a codegen struct copier library

I think using the yaml library directly would be a lot easier. You could then unmarshal both configs to a struct and use something like copier to update the values.

However, if you don't want to bother, I suggest to take a look at https://github.com/jinzhu/copier which is more extensive and works with slices and pointer types.