I work with a lot of dynamic data in {{date, datum}. . .} format,

datedatalist={{{2001, 1, 1}, 45.2}, {{2002, 1, 1}, 132.}, {{2003, 1, 2}, 121.1}};

and I have historically attached a header to each object in a format like

datedataObject={{header version, data series name, type (value, % change, etc.)}, datedatalist};

I can see advantages to using Mathematica's TemporalData[] type, and to using MetaInformation[] for recording the header. I would set this up with something like

newObject = TemporalData[datedatalist, MetaInformation -> {"name" ->"whatever", "type" -> "value"}];

and extract header items with, for example

newObject["name"]

But this leaves me with two puzzles,

1. How do I add MetaInformation after the object has been created? and
2. How do I change existing MetaInformation?