Yeah you are right
i figured this out before your reply, it's all the morning im playing with the camera trying to figure out things
In fact it overrides the aperture, and in the report the camera give after the shoot, it show the correct aperture used. In any case it seems the maximum aperture limit of the camera is 11 (instead of it's default 8 ) .
I would use the default apertures myself too, but im reading and trying to do the exerces of the "understanding exposure" book by bryan peterson, im new to photograhy, so every bit of aperture or shutter time i can use help to experiment
But i find difficult to use these custom settings because like you said, i cant see changes on screen so i have to shoot photos somewhat "blind". In fact i think to open another topic to see if someone can help me understanding better the misc and dof indicators of chdk to learn to use them instead of those of the camera, because like this is a bit hit or miss!