can be preview.type programatically changed via an action?

Hi all, it looks like

set(preview.type,"");

doesn't work,
is there other way to change the preview type, w/o loading a scene ?

also I'll need to set it back like

<preview type="grid(cube,16,16,256,0x888888,0x000000,0xFFFFFF);" details="1" /> 
then 
<preview type=""> 
then again 
<preview type="grid(cube,16,16,256,0x888888,0x000000,0xFFFFFF);" details="1" />

thanks,
Dorin

Thanks Klaus, appreciate the quick reply.

Then left me no chooice but to have two dummy scenes with different type and nothing else, have all the hotspots globally with keep=true, and to load the scenes with KEEPALL like on/off grid .
Just tested it and works perfectly, the switch is instant

cheers,
Dorin