The bulk update request #10571 has been approved by @evazion.
It's like the raven vs crow debate. It's essentially the same thing. Most posts under rat aren't even depicting particularly large rats.
Note that the japanese language doesn't even distinguish between the two, they just slap 鼠 on both, so any pretense that artists of all people can tell them apart is a joke.
At a minimum this should be an implication, but from a glance at the tag it doesn't even look like people can tell them apart, so they are functionally equivalent.
Updated