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 becomes high? sure, it happens all the time. Pop art is an example.
can high become low? it's more difficult but not impossible.
For example, can the painting 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 has to do with 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.