Paste background noise recording into selection

[steve]

What I would like to do is create a macro that lets me paste the background noise into a selection.

There’s already a plug-in available to help you do that:

Punch Copy/Paste

A pair of plug-ins for simplifying “punch in” editing. Unlike the standard paste function in Audacity, the “punch” paste replaces the selected audio with just the right amount of pasted audio to match the duration of audio being replaced, thus the speed and timing of the track is not changed by pasting. These plug-ins were developed from a feature request on the forum (https://forum.audacityteam.org/t/alternate-equal-length-paste-command-resolved/28836/1) to streamline the work flow of replaci…

(actually it is two plug-ins, one for copying and one for pasting.)

The user documentation for is in that post.
Installation instructions are here: https://manual.audacityteam.org/man/installing_effect_generator_and_analyzer_plug_ins_on_linux.html#nyquist_install
(It’s a “Nyquist Plug-in”)