How to update a master project in Project Online via CSOM or REST?

I can update "regular" projects via the CSOM, but what about Master projects?

1. ProjectContext.Projects does not seem to include master projects. This also seems to mean that the following code works if ProjectId is a non-master. If ProjectId is for a master project, then ExecuteQuery returns nothing.

 var Projects = projContext.LoadQuery(projContext.Projects.Where(p => p.Id == ProjectId));
projContext.ExecuteQuery();

2. I can get master projects via a REST call. But then, how do you update them? The documentation suggests that it is possible to do CRUD operations via REST, but I can't find any documentation that explains how to actually do that.

Or, I am just missing something? It would seem that not having access at all to Master Projects would be a blocking issue for most?

Mike G.