Jean-Ignace Isidore Gérard (low)
William Blake (high)
There is also the consensus issue.
"high" refers to work that has been validated through the years. Generally stuff that belongs in museums. "low" is the opposite.
Now, can low become high? It happens all the time. Pop art is an example.
Can high become low? Let's see.
Imagine Les Demoiselles d'Avignon (1907), by Picasso, considered a masterpiece, become a much lesser work of art.
The answer is that it's possible. But unlikely. the reason is the undoing of consensus about art, which is not the same as consensus about science. the former is based on taste the latter is based on facts.