replacing starter boards
The only easy, (heh-heh), way to remove the bottom courses of cemwood shake/shingles is to buy a slate nail puller/ripper. It is a long flat bar with a "nose" projecting wider at the tip.
You slide it under the shingle product, and slide it sideways until it bumps up to the nail, then pull downward on the bar until it hooks the nail shaft.
When it is hooked on the shaft of the nail, you then use a hammer to pound the handle downward towards the eave edge, and the sharp ripping part of the tip of the bar will slice the nail in half loosening the shingle product.
When all of the nails are removed, you can gently slide the shingles/shakes out of their successive courses.
Then you have open free access to replace the boards that are termite infested.
Replace them as per standard installation practice, except for the upper most row that you had to remove. On this row, you will either have to use a gutter spike cobbonger to toe-nail the shingles in place under the next course of shingles or you will have to face nail them and rely on a good grade of caulk to make them weather-tight.
If you have to remove at least several feet of rows, you should install Grace Ice and Water Shield underlayment on the new boards which were replaced to ensure water tight integrity.