When saving a material with animated parameters (e.g. using an animated noise or reading a texture sequence) to a USD file the expressions are baked and we lose the animation. I understand this is the intended behavior of USD however it's not practical for lighting artists to add an Edit Properties node in each of their shots to re-create the material animation, they may not know which expression is needed either.

Is there a way around this? We can save multiple time samples but that's not really a solution as we'd still be limited to a specific frame range. This may be deviating from true USD but could we save a VEXpression to the USD file and evaluate it later in lighting to keep the animation alive?

In the hip file attached the mtlxadd_ANIMATED has an expression driving the value of Input 2, this is what I need to keep alive.

You have a warning on your mtlxAdd node. Try putting your entire material inside a subnet, promote the parameter you want to animate, then animate that value on the subnet, not inside the material.