Mark Tucker

The relationship actually goes the other way... Each value parm can have a "usdcontrolparm" spare parm tag to point to the parm that should be used as the control parm. Other than that, it isn't actually the name of the parms that matters, but the relative positions of the parms... Control parms affect all value parms that follow it until the next parm that ends with "control".

If you call `Get()` without an argument, what you get back will be the "default value" of the attribute. If the attribute you are fetching has time samples (or really even if it doesn't have time samples), it's always best to pass a time value to the Get() method. Passing in `hou.frame()` is always a good option but will make your node time dependent. Passing in `0.0` will work if there is a single time sample or if the value is only set as a default value, and will avoid creating a time dependency. But it won't give you the expected result if there are multiple time samples available on the input's stage at the same time.

The contents of the Layout LOP are not completely locked. You can dive inside the Layout LOP and you'll be presented with all the nodes that were used to load the assets from disk (probably a bunch of asset reference LOPs). You can modify these nodes to use HIP-relative paths instead of absolute paths. Things can go sideways if you nodes in there, or cause the primitive path where the asset is loaded changes, but otherwise modifying parms on existing nodes should be safe.