Is there any way to import / include custom glsl library files with the shader api?

I have been looking through https://substance3d.adobe.com/documentation/spdoc/shader-api-89686018.html but can't see any way to do this.

I have a number of custom shaders that all re-use a lot of functionality. This means that if I find a bug or want to update one function, I need to update all my other shaders too.

Is there a way to just create a 'library' of my own and import that? Currently it looks like the only files we can import are the ones that come with substance. 

Is there a way to get this working without having to maintain around a dozen files containing many of the same custom functions?

If not - is there any plan to allow for importing our own library files?

Thanks!

PS:

The docs do say "Please note that you can't edit it nor create your own at the moment."

but they've said that for a long time so I'm not sure if anything has happened on that front since the last time the docs were updated.

On that note - the docs do seem a little out of date as they still say you can get shaders on Substance Share and give a dead link: https://share.allegorithmic.com/libraries?by_category_type_id=6