Varispeed is very cool and I use it all the time to slow down projects tempos. It is playback function. You are bouncing the original audio and tempo - it will sound faster or slower based on the varispeed setting but just as the original track will sound faster or slower so will the bounce.... however the original has not changed. Here are the steps...( oh and remember though, if you bounce a mix - you will get the varispeed playback.... so for example if you have 5 tracks and you you slow down by 20 bpm - when you do a full bounce - the resulting file will have the adjusted tempo of the varispeed setting. So if you want a single track or region.... just mute the others and do a full bounce ( consider that your export).
If you truly for some reason want to do a regular export with the varispeed effect.... here are the steps ( I will just use one track for explanatory purposes but it applies regardless).
1/ Bring in your audio
2/ Turn on varispeed and set to what you want. ( remember the bpm)
3/ You can turn varispeed off now.
4/ highlight the track or region in you want to export.
5/ track-tempo- beat detection. on the region/track you select above... ( you don't need any options just run the command) when done....
6/ In the region inspector -> check follow temp & pitch (this won't be there until you do step 5 unless you external audio had tempo information in it already)
7/ Change the BPM of the project to whatever BPM varispeed was at prior to turning it off....
8/ playback the track to comfirm it is now at the adjusted tempo
9/ Export audio.
Export will reflect new speed..
You can also do it with flex - but let's start with this first. Let me know if in fact the above procedure did in fact answer you question....