Overriding templates.yml as primary templates file

Is it possible to non-destructively (not fiddling with the install files) way to change what the primary template file is?
The reason being is that I want to leave the core templates.yml alone and override/add to it with a project-specific template file. This project-specific one will include templates.yml.

I want to be able to allow the templates.yml to be upgraded in the future and should be generally left untouched.

Is there perhaps a better way of going about this?

Thanks!

Why do you want to do this, instead of templates.yml including the other files that will change frequently? Seems like a needless complication.
Also, if your config is managed with git, merging changes between projects is much less painful.

One use case is handling client ingest/delivery paths. It seems like overkill to need to maintain an additional pipeline config for just adjusting a template for either ingestion or delivery templates.

I do not question the need for branching configs for different projects, but it seems easier for templates.yml to include the other files, and the other files would be changed, instead of the opposite.
If managing through git, it doesn’t matter too much whether these templates are in a separate file, though. The client’s paths are just patches to the main file (or one of the included).

The question is more conceptual than technical - how do you want to separate your templates by “concern”?