They may take into account improvements on individual properties as evidenced by building permits, but the chances of them actually seeing your property is remote. And every property is unique. Do not challenge any assessment unless there are clear grounds for reduction, and unless you prepare thoroughly. You will have to spend many hours preparing your appeal, in order to do an effective job. That is the reason many landlords choose to have a licensed appraiser take care of the appeal for them.
Some landlords figure that their time is better and more effectively spent doing something else.
Besides, appraisers' fees are tax deductible. Regardless of the time involved, in addition to saving money, there are some excellent reasons for taking care of the project yourself. The primary reason is practice. Going through the appeals process once gets you pretty good at it. Then if you ever have to do it again, it will be infinitely easier.