From what I understand, a bracha rishona is valid bedieved (i.e. you shouldn't make that blessing... but if you did, you don't have to make another blessing before continuing to eat) if it is an appropriate description of the food. For example, haadamah is valid for fruit or bread, because the tree or wheat stalk grows out of the ground. Haetz is valid for grape juice, because the grape vine is a variety of wood/tree. Shehakol is valid for everything, since everything was made by God. Mezonot is valid for most foods (don't remember exactly which) since "mazon" is a generic word for food.
The opposite is not true - haetz on a vegetable is simply invalid, since it is a false description, and you must make a new blessing.
If you want to eat a fruit and a vegetable together, and you said "haadamah" - my recollection is that it only applies to the vegetable, and you must make a separate blessing on the fruit, because we presume that the blessing only applies to the things it is supposed to apply to. Whether you can overcome this presumption (i.e. by saying out loud what you intend) may be a debate in the sources.
Everything I said applies to the blessing before food. As for the blessing after food, I don't know, but I would suspect similar rules apply.