Ah. Ok. channe() and range() can’t be set dynamically. Those identifiers are intrinsic to how the parameters work, and VST hosts need to know what they are when the instrument is first loaded. This is actually somewhat related to a recent post by Oeyvind about dynamically creating widgets.
Changing these dynamically will cause unwanted and unexpected behaviour in a host. I know in this case you are not using a host, but I really think it’s important that instruments behave the same in standalone Cabbage as they do in a VST host. Do you know what I mean? It’s unfortunate, but I think it will only lead to confusion among users if things are different in one interface than another. Cabbage is a toolkit for generating plugins after all. Even the instruments loaded by Cabbage itself are treated as plugins.