There is no ‘official’ way to do that, but it would be possible to hack the AUP file.
For an overview of Audacity’s “project” format, see: Managing Audacity Projects - Audacity Manual
Here is a very simple project, just one 10 second audio track with a Time Track and 3 control points in the Time Track:
<?xml version="1.0" standalone="no" ?>
<!DOCTYPE project PUBLIC "-//audacityproject-1.3.0//DTD//EN" "http://audacity.sourceforge.net/xml/audacityproject-1.3.0.dtd" >
<project xmlns="http://audacity.sourceforge.net/xml/" projname="timetrack_data" version="1.3.0" audacityversion="2.2.0-beta-Sep 25 2017" sel0="0.0000000000" sel1="10.0000000000" vpos="0" h="0.0000000000" zoom="88.3500000000" rate="44100.0" snapto="off" selectionformat="hh:mm:ss + samples" frequencyformat="Hz" bandwidthformat="octaves">
<tags/>
<timetrack name="Time Track" height="100" minimized="0" rangelower="0.900000000000" rangeupper="1.100000000000" displaylog="0" interpolatelog="1">
<envelope numpoints="3">
<controlpoint t="0.000000000000" val="1.000000000000"/>
<controlpoint t="5.019807583475" val="1.100000023842"/>
<controlpoint t="9.977362761743" val="0.997826099396"/>
</envelope>
</timetrack>
<wavetrack name="Audio Track" channel="2" linked="0" mute="0" solo="0" height="150" minimized="0" isSelected="0" rate="44100" gain="1.0" pan="0.0">
<waveclip offset="0.00000000">
<sequence maxsamples="262144" sampleformat="262159" numsamples="441000">
<waveblock start="0">
<simpleblockfile filename="e00002f0.au" len="262144" min="-0.8" max="0.8" rms="0.565686"/>
</waveblock>
<waveblock start="262144">
<simpleblockfile filename="e000061f.au" len="178856" min="-0.8" max="0.8" rms="0.565685"/>
</waveblock>
</sequence>
<envelope numpoints="0"/>
</waveclip>
</wavetrack>
</project>
Another possibility would be to modify / extend this “slied-speed” Nyquist plug-in: Slide effect - HELP NEEDED - #8 by steve