You are correct about those functions not including CC data. In your stated example however...
I had to change the tempo from 140 to 70 bpm,
The midi clips, if they were already on the timeline, should have followed the tempo changes and automatically sized to half speed, including the CC's, assuming the instrument track was set to "beats" in the Inspector. If they weren't already on the timeline, yes, you may have to manually stretch them to half speed to keep the CC data lined up.