So you have metadata at the column or table level but it will be common across a lot of the tables and columns within a model/project and you don't want to update it in a ton of places if you make a change?
The way I would do it, would be to create some non-generated 'template' objects and a script to copy the values there to other objects. You can centralize those template objects in another model if you want.
If you add a property on each table to point at the object it got its defaults from, you could create an update routine to copy the new values down when you make a changes (or use an event to auto-update when you open the model). We've done something similar in the past.