I successfully protested my assessment a few years ago.
I had put a new roof on and because of the permit, they raised value by about 10%.
I disputed and provided compatible home values and recent sales to show that they were crazy.
I also commented that a new roof was not an increase in valuation, I was bringing the home up to past condition.
Here is the county website to search your property and find compatibles.
I did mine a few years ago and won. I did not do anything crazy but it paid off since the other homes in the hood are valued at more so when the downturn happened 08-09 I was ahead of the game. The only raised mine 8% but I need to look at the comps in my area.