I have a project from many years ago and several versions ago that consists of both midi and audio tracks.
It's not lining up with the metronome, but it's in the ballpark.
 
Is there a way to change the projects tempo without having all of the midi tracks "adjust" to the tempo change?
I've never had to do this before and I'm not sure the best way to attempt to get the project back on the grid.
 
 

Set Measure/Beat At Now (Shift+M) will calculate and insert a tempo to make the specified measure/beat hit the Now time. MIDI event times and durations are re-calculated so that the absolute playback timing is not affected; the timeline shifts around existing MIDI and audio.
 
If the first MIDI event starts at 1:01:000, all you have to do is set the Now time on the downbeat event corresponding to 5:01 or 9:01 using tab to MIDI, hit Shift+M and enter that measure and beat to get started. Then you can set additional points as necessary to keep it locked in.
 
I use this feature often to time-align MIDI improvisations recorded without a click. My favorite SONAR feature.