Software that can partiall rename files?

I am using software that generates a rather large number of files (172 files in just 10 minutes work, I plan to be working on this for many days), but for them to work with another program, I need to partially rename them.

A sample of what I need to do, would be :

TestingWorldSpace000.4.3.1.DDS
TestingWorldSpace000.4.3.1._nDDS
TestingWorldSpace000.4.3.2.DDS
TestingWorldSpace000.4.3.2._nDDS

-Rename to-

TestingWorldSpace.4.3.1.DDS
TestingWorldSpace.4.3.1._nDDS
TestingWorldSpace.4.3.2.DDS
TestingWorldSpace.4.3.2._nDDS

The usual method of "Select-all, F2" just renames them to something like "TestingWorldSpace.4.3.1.dds(1)" for each and every file, which does absolutely nothing.
At the moment I am doing it by hand, but when I reach into the thousands, tens of thousands, maybe even the hundreds of thousands of files, I really, REALLY do not want to rename them by hand.

Anyone know of a program that can do this?