Geoff, are you saying...
If: You manually enter a new slope constant in the Power Control (head unit)
Then: the Power Control (head unit) sends a signal to the Power Meter, which changes the slope constant stored on the Power Meter.
And: This new slope constant stored on the power meter is what a Power Control (head unit) will detect (in future) when in "auto detection" mode.
Sorry for missing this (Canada Day, etc.) I also think that this answer may cover-off some of the other stuff you have asked. The answer is a qualified 'no'.
The 'auto-detect' feature is unique to the wireless SRM PowerMeter (i.e., not found on wired PowerMeters), so by default, only the PC6 and PC7 PowerControllers can 'benefit' from it. When you change the slope in manual mode using the SRM software, the slope stored in the PowerController is not then changed so that the 'auto-detect' feature will, thereafter, apply the new slope. Rather, the PowerMeter will default to the original, factory slope setting.
I know. It's lame. I imagine that this will lead to another round of comments about SRM seeking to further secure 'repeat' business. There is a way to do it, though...