Adding/removing host-visible state (parameters) isn’t really supported by any host, and with ones that do you have to be extremely careful about parameter indexing. See a recent discussion about a similar issue for renaming parameters, which is rife with issues in itself (much less adding/removing, which I can’t even fathom).
In the case of AudioProcessorValueTreeState, you can’t mutate the number of parameters after you’ve set the ValueTree. So you’d be stuck to a fixed number of host aware parameters (which is appropriate for most if not all plugin types i.e. VST2). HOWEVER, you could totally add a non-host-aware set of fully modifiable state maintained internally by the plugin (and not visible to the host) which could mutate the number of audio clips.
Hopefully that helps.