You can overcoat with Pettit Vivid. Vivid is a hard ablative and I was told by Pettit tech support it is compatible. In my test (a small sample approx 3x3 feet) it adhered well to Micron Extra -- no issues after 2 years.

I'm currently using Pettit Hydrocoat which is probably also considered soft. I like it because it's water-based (low VOC) and half the price of the others, and just as effective.