Randomly increasing the open area might make it louder but it could also affect the frequency response, loading on the driver, etc. I think you'd also want to make sure that the actual driver extended beyond the area of the existing slot, you could be opening up areas that have nothing to do with the speaker or even essentially be drilling holes in the speaker enclosure.
In other words, it could help but it could also make things worse, perhaps a little more research would be appropriate before actually trying it.