if you want to hack Ghost core you need to follow

https://docs.ghost.org/docs/working-with-ghost and

https://docs.ghost.org/docs/working-with-the-admin-client

Once you done all your hack job, just run grunt release command under your ghost folder.

grunt release

Once it completed, you will get a zip file:

./.dist/release/Ghost-1.16.1.zip

Then run your hacked ghost under a new empty folder:

ghost install --zip /path/to/.dist/release/Ghost-1.16.1.zip

--zip Path to Ghost release zip to install [string]