Reduce Extra budgets in Change Orders

Hi,

We use change orders in project accounting to track changes in budget. Recently we found that we can reduce extra budget of a cost category where costs already incurred and system does not popup any notification.

To make it clear we have a cost category where budget is $ 100 and actual cost incurred $ 70. Now if through change orders we reduce budget for $ 31 then system did not give any alert, that budget would be less than actual costs, as we get notifications in case of 'cost exceeds budget costs' under certain cost category.

Please suggest how to fix it.

Regards.