With the suggested approach in this talk, a dedicated source EA project is used to define the scripts. Once a qualified version is ready to be published, I have to export the scripts via the Export Reference Data function, and import the generated XML file on the target EA project. However some of the script groups are not aimed at being released to the client since they've been used for development purposes e.g. to test a specific EA API method. As discussed at presentation, this can be catered by using a blank EA project to remove all unofficial scripts, before publishing it on the live EA project.
As an alternative to this solution, I tested a new tool published by Geert Bellekens, EA Reference Data Splitter. This free third-party tool does not require to open EA (contrary to add-in extensions).
Once opened (see above), the reference data XML file, generated from the source EA project, needs to be selected. All the scripts are listed in a tree structure. The scripts to publish must be enabled before generating the XML reference data to be used on the client's project (see all "Project..." groups).
Result: the expected list of published scripts is available on the target EA project (in addition to the built-in EA scripts).
This tool may support in the future additional reference data such as images.
Note: a similar feature already exists in EA for the searches i.e. it is possible to export a selection of custom searches.
EA Reference Data Splitter tool is available to download here.