An existing tenant will renegotiate. Due to lower rent, the tax authority may reduce the property tax .

The answer to this question resides in your lease document. You can write the lease so that reductions in operating costs do not affect the amount of total rent you are collecting. Increases are usually covered, yes, and most leases will not let expenses drop below the base year. So, if taxes decrease there is not a requirement to reduce or credit tenant. The LL argument is that those funds are required to maintain the property at the same level as the base year or beginning year. In a renegotiation, I would keep base year the same as primary term unless I needed to entice the tenant somehow and allowed a benefit to Tenant based on the tax reduction. Good luck.