I am looking for a tutorial or something on a workflow to modify external library that I use in my project. So fork it, change it, test it, pull request. Can I just change it somehow in my main project? Or do I have to clone it in a seperate project per library? (Using IntelliJ IDEA CE)

Intellij supports importing more than one project. Also, is this jvm, Android, native? Do both projects use gradle or something else for building? If gradle for both, look at composite build in gradle docs and intellij supports it.

Multiplatform, but in intellij. I use gradle. I'll look into your leads, thank you