I have a bunch of square symbols that are all the same size. I would like to set random pre-designed symbols into a defined grid.
Symbols placed randomly within grid:
Is this at all possible?
Using the search terms "illustrator script random position," I found a number of possible solutions. One of them is a canned script from vectorboom.com in their free scripts section. It appears to allow to produce your objective.
Another result is an answer within this SE. It also appears to solve your goal, but is not as obvious to the eye.
There may be other solutions presented via the above-noted search terms.