Can I change the tempo of a project without affecting the audio?

Absolutely!  The only time your residing audio would be affected by a tempo change is if it were an acid or groove clip.  So, the audio (transients) will all stay as originally recorded or imported regardless of the tempo change or tempo of the new project.
 
Kind regards,
 
tecknot

Audio tracks will appear to change length because the M:B:T grid is the absolute visual reference, but they will play back the same.
 
The only thing that will cause an issue are clips that don't start at 00:00:00:00. This is because the default timebase for both MIDI and Audio is MBT, so their start times are locked to measures. You can change all their timebases to Absolute, but the easier way is this:
 
- Snap the Now cursor to the beginning of the measure corresponding to the Current Tempo + 1 (101 in your case).
- Hit Shift+M to open the Set Measure/Beat At Now dialog and enter Target Tempo + 1 (89) as the measure, and OK.
- SONAR will change the initial tempo to make the timeline hit that mark at that absolute Now time without changing the absolute timing of anything (including MIDI if any).
- In case you're wondering, the "+1" is needed because measures are counted from 1, not 0.
 
 

2 Completely different ways, both of which work perfectly
 
Good work men!

headsnack
Thanks so much to everybody!  I honestly prefer the first method of changing the measure.  Even though an audio bounce should be clean, I'm always weary of having multiple tracks of bounced silence in my compositions. 

Understood.