I.3.1. Screwed-on chainrings
The only thing you should consider if replacing screwed-on chainrings: chainrings with 40 t. or less have to be turned out in the inner diameter by 2 mm (inner diameter must be 96 instead of 94 mm).
If not, you can't mount the chainring on the left side of the spider.
All Schlumpf chainrings come with the adequate inner diameter.
Hint for easy tighting: Put a little portion of grease on the threads and the nut won't spin. Done so, it's easy to tighten the screw to the correct torque.