The only way is to save the component to file and load that component in another file. Any attempt to share entities between models will either result in crashes or corrupted models.
Unfortunately we don’t have SUComponentDefinitionSaveFile - that is on our list to include in a future release.
Meanwhile you can use SUComponentInstanceSaveAs. But beware - this function has some unexpected side-behaviours: it bakes the instance transformation into the definition transformation. It also makes that instance unique.
So I would suggest you use SUComponentInstanceSaveAs on a model which you don’t need to save afterward. And you might want to reset the instance transformation in order to save the definition without the instance transformation applied.
From your source model, use SUComponentInstanceSaveAs to export the components you need to “copy” (but remember what I mentioned about the instance transformation when using SUComponentInstanceSaveAs). Then in the target model use SUModelLoadDefinition to load the exported components as new definitions.