Overview
I had the opportunity to publish a customized Mirador 4 as an npm package, so this is a memo of the process.
Fork
Fork the repository from the following official site.
https://github.com/projectmirador/mirador
The result looks like this:

Create a Branch
Clone and create a branch.
The following output appears:
Development
Make modifications as introduced in the following article.
Test
Test to confirm there are no issues.
Commit
Merge
Switch back to the master branch and merge the contents of feature-add-immediately-property.
Push
Push the changes on the master branch.
Publish
Use the following command to temporarily ignore local changes. (There may be a better approach…)
Change the package name to a different name.
Publish.
As a result, it is published as follows:
https://www.npmjs.com/package/@nakamura196/mirador
Summary
Regarding pull requests for the changes, I plan to do this separately after investigating the impact of the modifications made this time.
Some steps included here may not be ideal, but we hope this serves as a useful reference.