Adding addresses not recognized by our tax rate vendor (Vertex)

We plan to enter addresses that our taxing vendor (Vertex) does not recognize as a valid taxing authority address. We also plan to use the tax rate of surrounding cities for theses customers that we need to add / enter manually. If we set up a tax jurisdiction and tax rate will we be able to update this information going forward.

We aanticipate the ratae for this set up will change periodically so we need to be sure we can change the rate when we need to.

We are on R12.1.3.

Also, with the ability to write rules in Ebiz tax, is it possible to create a rule for each additional address manually entered that would automate the updating of the tax rate going forward, based on a surrounding / close by cities rate? If possible and anyone has ever written such a rule, can you give an example of how it was constructed?