URGENT: How to change Regional Settings

The problem is that we need to keep two regional configuration just for a couple of months while we replace the old system with this new one. Its extremely difficult to examine the whole code looking for each thread created because this is a complete system for a big company and it is conformed for more than a thousand of assemblies running on different physical layers and performing a wide variety of operations. Actually we are at the begining of testing stage with lots of users applying every kind of tests to every little functionality of our system so it would be easier to find where the applications fails if we change the overall environment than examine the code that was written along the last 2 or 3 years.

Wouldn't it just be worth it to man-handle each thread into the culture you want so you take out any possibility of errors based on implicit inheritence of cultures? Seeing the behavior you have, I'd be more eager to ensure each of the threads are as I want them rather than trying to change the overall environment and hoping they conform.