A “normal” Nyquist effect acts on the selected audio, but there are also “Nyquist Macros” (see: Nyquist-Macros - Audacity Manual)
Note that this is an area of active development and the documentation is still being written.
See this topic: Why Are New Tracks Always Added to the End? You Should be Able to Add Them After the Selected Track
The plug-in “trackmove.ny” moves the bottom track up to one below the track that currently has focus. Feel free to adapt the plug-in to suit your needs. If you get stuck, start a new topic on this forum: Macros and Scripting - Audacity Forum