Hi.
Just came around this post. I own the HX Stomp and missed the function to reverse-play the recording. I simply tried the cc-messages of the above post ( CC65 0-63: Forward; 64-127: )Reverse) and can say that it works. I have Firmware 2.82. Btw. I sent the cc-messages via command-line with the fantastic tool named "sendmidi" from a dutch guy. The command goes:
c:\sendmidi.exe dev line cc 65 65
Hope it helps.