Suppose you need to add some_dir/your_file.txt to META-INF using Maven, so that the final path looks like this:
To do this, you need to create a META-INF/some_dir folders in the src/main/resources directory, and put there your_file.txt file:
src/ main/ resources/ META-INF/ some_dir/ your_file.txt
Once compiled, Maven will move META-INF/some_dir/your_file.txt from resources to the right place without deleting the existing files in META-INF inside your jar.
If you still have any questions, feel free to ask me in the comments under this article, or write me on firstname.lastname@example.org.
If I saved your day, you can support me :)