This article covers how to pull scripts from multiple projects and import them into another project. You can even use this to make container bound script standalone, or visa versa. … This article will cover the library that does all that, along with various other usage examples – for example, pulling in code snippets from or libraries, merging manifests, or testing add-ons.
Some more magic from Bruce Mcpherson this time creating and documenting a library that can be used to copy/replace scripts. Bruce’s illustrates this with an example of pushing a standalone script to a container bound Google Sheet project and I’m sure you can find many other ways this could be useful to maintain script projects.