Subject to the provisions of chapter 137, in addition to the tax rate increase allowed pursuant to subdivision (3) of subsection 5 of section 137.073, if an ambulance district voluntarily decreases its tax rate duly authorized pursuant to section 190.040 or 190.041 in any tax year, such ambulance district may in any subsequent tax year increase such tax rate, without voter approval, to the rate previously authorized pursuant to section 190.040 or 190.041.