Unfortunately, due to the community-based nature of the platform, we do not have the resources to support past versions, but it would be great to make useful components compatible with the latest version. Could you please try the module in Slicer 5.0.3 and start to get past the errors? Most of them will probably be trivial, and with the rest we are happy to help you. This would be a great contribution!
I’ve updated the extension for Slicer-5.0.3, added a short step-by-step tutorial, and submitted the extension to the Extensions Index so that from tomorrow it can be installed by a few clicks from the Extensions Manager (extension name: SkinMouldGenerator).