Using the Flygprestanda TL charts does not restrict the use of assumed temperature when following the improved climb speeds.
The Boeing Performance Tool for the computer allows for the same procedure.
As a matter of fact, the BFT gives you very high speeds always as it prefers the improved climb speeds. A lot of temperature reduction reduces the "sweating" for the engines. In the upper temp range I saw that 1 degree assumed gives about 5 degrees reduction in the engine, a lot when you think about 10 - 20 degrees assumed temp reduction, as is often possible.