Hello,
For the new table (C): you will want to start synchronizing this table from scratch, this will cause all the applicable rows in table C to be downloaded on the first synchronization. You can acceive this by having table C in a new scope.
For the table with an added column (A): You would want to add the column on the server and client without modifying any tracking metadata. Does the column you are adding have a valid default value?
--
Kyle