7-bit data mode in bluetooth module rn-42
I contacted microchip support team, here are their answer:

Problem Resolution: 
Hello,

I found that 7-bit data mode does not appear to be supported by v6.15 firmware. This has been captured as a bug, though I don't know if or when it will be added to future firmware. I'll ask that the release notes be modified to include this limitation.

If 7-bit data mode is required, I'd recommend ordering modules with v4.77 firmware. This can be done by contacting your local Microchip sales office. 
The part number is: RN42-I/RM477

Best regards,