@ono, Thanks for your question. One of our main goals was to maintain compatibility with Qt user code. We have worked with a significant number of projects who migrated to CS and no one lost functionality. Most code will work without any modifications.
We have a parser (PepperMill) which you run one time to convert anything in your header files which used moc. For example, we change Q_OBJECT to CS_OBJECT(class_name).
Here is a link to the macros which are modified.
https://www.copperspice.com/docs/cs_overview/m_macros_metaobj.html
@ono, In terms of using an existing library, if it is a C++ library this works great. If the library was written using Qt it will need to be migrated to CopperSpice. This has already been done for a few libraries.
Our CS team has experience with library migration and we are available to help with this process.