gswitz
Only thing I know of are the things I've described.

 
I was afraid you'd say that. Now I have a $150 feature request if it ever gets added to the new Sonar 2015 but I would gladly upgrade if they added a feature to just change tempo to half or double time and left everything else in Absolute time or if they added options to the Tempo change window with selection boxes for what should and shouldn't get changed, similar to the Project > Insert Time/Measure window.

Well, maybe Bapu's suggestion fits your case best.

GotMetalBoy
Instead of changing the whole project, just to import a few MIDI clips, is there a way to just change the Tempo of the MIDI clip from 91bpm to 182bpm?

 
Load the SMF into a dedicated midi editor, change the tempo and save it to a new SMF file. Be aware though, that if the PPQ of the file is an odd number, some notes may go slightly out of time.
 
I don't remember the name of freeware one I use for this. I'll post it when I get home and look, but I think you can probably find one via Google. :)

Once you have all the markers set to SMPTE time, the following trick will change the timeline tempo around both MIDI and Audio without affecting the absolute playback of either, and it's not necessary to change the Timebase on anything:
 
1. Snap the Now time to measure 183 (current tempo +1)
2. Hit shift+M to get Set Measure/Beat At Now dialog
3. Enter Measure 92 (target tempo +1)
4. OK, and SONAR will alter the initial tempo to make the specified measure hit the specified Now (absolute) time.
 
I haven't tried it with markers, but I think it should leave them alone if they're set to SMPTE.