See the descriptions of two scripts on
this page and
this page named "ReplaceWithSymbol" and "RandomReplaceSymbol".
ReplaceWithSymbol replaces the objects in the current selection with instances a Symbol of your choosing that exists in your Symbols Palette.
RandomReplaceSymbol randomly replaces selected Symbol Instances with Instances of the other Symbols in the current Symbol Palette.
So with those scripts, there are several ways to approach what you describe. For example:
1. Put any Symbol Instance on the page.
2. Use Transform Effect to create your grid.
3. Expand the Transform Appearance.
3. Use RandomReplaceSymbol to swap out the Symbols.
or
1. Draw a rectangle (or any other shape).
2. Rasterize it.
3. Use Filter>Create>ObjectMosaic to create a grid of rectangular paths. Ungroup the results.
4. Drag a Symbol Instance (any will do) onto the page.
5. Select everything and run the ReplaceWithSymbol script.
6. Select the array of Instances and run the RandomReplaceSymbol script.
...and so on.
JET