I'm writing an asset postprocessor that tags objects if their name contains one of an array of strings. Every time I create a new scene for this project, I have to add all the tags by hand. There's quite a number of tags and to keep the manual labor to a minimum (coders are lazy, right), I'd like to create the tags by script.
It sounds like you would be better off creating a prefab for each object that you put into the scene, with scripts and other components included, then add a tag to that prefab. Then when you bring the object into, the scene, it will automatically have the tag.
That way all the objects are pre-tagged and any scripts you would have to put on them are already there. It can save you a lot of time.