This is speculation only based on the (OP)'s question:
However, the "Dark Energy" would not have to, as you put it, radically change its behavior. The "Dark Energy" is doing what it is suppose to do, expand Space-time in the presence of matter. And Inertial Mass Gravity is doing what it is suppose to do. Cause Inertial Matter/Mass to clump together.
What this model would suggest is that there is another Force and Energy out there that counter acts the "Dark Energy" over long distances. I propose that this energy is called the "Heat Radiation Gravitation" energy of space-time. The "Heat Radiation Gravitation" energy would cause the expanding "Dark Energy" to become diluted, and loses its grip, and finally becomes weak over great distances.
Once again, this is total speculation, however, there is some evidence for the above, and is meant for discussion.