Is it possible to to work with metaclasses defined for catalog models in context of CatalogService.svc?
For example I want to create catalog entry (product/variant) that has my custom metaclass(set of custom fields). Can I do this with CatalogService.svc interface?
Just to clarify, am I able to put metadata values by CatalogService.svc?
Unfortunately, this is not supported through CatalogService.svc. You'll need to use other way, such as through Commerce Manager to archive that. CatalogService.svc (or more general, ICatalogSystem) can only be used to manipulate entries, not define themself.