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.

http://land.elpasoco.com/


HTH
Roger