Can the node of the model set the transparency?

1. A concise explanation of the problem you're experiencing.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

Right now it’s not possible to set a model node’s transparency after the model has been loaded. Do you need to set the transparency dynamically?