If this driver does make it into the next program update, will that cause any difficulty for those of us who've already downloaded it? Would the program update (I've got it set to automatic update) recognize that the file's already installed?
Absolutely. The updater can handle much worse situations than this!

It will work seemlessly...
Actually, my only concern is that with the next
VPS update (probably due tomorrow), the updater will actually
repair your replaced driver as well -- i.e., it will re-replace it with the original version...

Watch for this - if avast prompts you for a reboot after the next VPS update, it's quite likely that this is what really happened. In this case, you'd have to download and replace the fixed file again...
Hope this helps,
Vlk