Is there a way to update the scriptnode UI with the relevant new parameter
Not without hacks. The best way of thinking about this is a black box communication of parameters into the node. Now if you want to update a UI state that you display on the plugin interface, global cables (and their data callback) are the way to go, there you can easily pack everything up into a nice JSON and send it back to HISE Script (on a deferred thread!), but I wouldn't recommend going the extra mile of updating the internal scriptnode parameters only so that you can look at them in the network with the right value.