You'll want to use the advanced random plugin to either generate a permutation table, which allows for non repeating sets of numbers, weighted probability tables also from the advanced random plugin, or simply save and check to compare the previous prefab with the current one and reroll if they are the same.
A more robust solution could use these methods together.
Thanks for the reply oosyrag
I didn't know advanced random was a native plugin. I'll check it right now and read its documentation to see if it covers my needs.
Probably the terms you mentioned aren't that difficult to grasp but they are a little scary for a coding noob as me.
Again, I'll try that and post the results or (more probably) the problems I'll encounter.
Cheers