Ok, I found the solution for Windows-Side:
When opening a font with FontForge, there (in GridFitting-Options) one can set certain attributes for certain point-sizes, such as Antialiasing. There is even two special columns for giving attributes to ClearType. These settings will be respected by ClearType, so no need to switch it off.
On Linux based OS, I still am no further, except that I know that some sort of fontconfig is what Qt5 "reads" and therefore decides. Unfortunately the Linux-RenderEngine ignores the above mentioned internal font-attributes.