Is is possible to change a material in a rezzed object as 100% transparency so it is really invisible?
The closest I found is the Transparent shader but that is good for phantom/glass like objects.
Other than that, if you try to use a fully transparent texture with the Standard+Alpha Mask shader this will complain that it's not possible.
Just 1 pixel, outside the uv area it's enough το "befool" the upload system. I uploaded a cube with a single pixel 10% filled with colour and you can see the result in the photo: a transparent object without shadow.
That trick works perfect, thanks Luise
Set the alpha texture to the alphablend shader, adjust the shader Mask to 100% and the Softness of the mask to 0% will do the same thing.