Texas is not a full disclosure state, therefor you do not have to let the appraisal district know how much you paid for the house.
If you feel your appraised value is too high, compared to the market value of your home, you can argue the value. You can hire a company that does this for you or you can do it yourself. If you would like to do it yourself, get recent sold information and take it to the district office. You may only do this during the first few months of the year. I am a Realtor in Houston and send my clients comparable sold prices if their appraised values are too hign.