No there isn't away and personally why would you. Years ago it changed over to Pay As You Go and could end up very expensive so this is a far better solution. As for "does it without asking", you gave permission when you signed/approved the contract. I guess now you have to managed the allotted monthly data allowance better to stop such automated conditions being applied.
caaf is correct, there is no way to turn off the $10 per extra 1GB system. This condition is outlined in your plan. If you don't want to be bumped up, you'll need to make sure you do not exceed your allowance. The best way to do this is to be careful in your usage after the 85% warning alert has been sent. Also, if you're using an android phone, you may be able to set a limit on your usage in your settings. Please let us know if you have any further question!