I don't know if there's a way to do it for a whole session or not; if you need to do it for just one distribution, you can just double click right over the value (say, mean = 0.124525) then Format --> Fixed Dec). That will change the number of dec. places shown. I've been looking around in the preferneces, but to my knowledge I couldn't find a way of making that fixed.
Now, if you need to run through multiple distributions in a given sheet, what you can do is run 1 distribution, change the number of decimal places as mentioned above, then click on the red dropdown --> Script --> Column Switcher. Select all the columns you want to see distributions of and that should show you statistics only with the desired # dec. places. If you need to do it for multiple sheets, one single column, changing it once and then copying the script might be faster.
LG