Custom webpack config

I need to add some lines in the Webpack config, but I don’t want to edit Sage files to avoid issues when updating in the future, and to be clearer for maintainers that this config overwrites the default one. I’m encountering this issue: NPM issue · Issue #324 · janpaepke/ScrollMagic · GitHub.

How could I do this? Would it be interesting to add this feature to Sage (maybe with config.json)?