Fellow Tax Protesters, Gather round

New to TX – Purchased last year in July 2022 and getting hit hard 20%+ on this year's assessment.

Has anyone successfully navigated the DIY ifile/isettle (or paid professional route) in getting their tax value protested lower than the sales price? We overpaid aggressively and have the appraisal from the financing as a much lower value, of which I would be happy if accepted as the opinion of value.

Are we powerless even with the supportive appraisal and market comps due to the actual sales price? If the process is completely hinged to that, it doesn't seem like a commercial firm protesting would be helpful either.

I received the homestead exemption on paid 2022 taxes by way of previous owner and have filed under my name for 2023. Is there any way to retroactively file the 2022 under my name to receive the 10% cap on this year's value assessment?