I posted this question to the Yahoo BC2000 group, but having discovered that there's a forum here at Mountain Utilities I figure it probably makes more sense to have this conversation here as it is BCmanager specific.
I followed Royce's advice from the Yahoo group and had a good look at the JX8p preset made by Rainer, and read his text notes as well. Feeling comfortable I loaded his preset into BCmanager and decided to completely re-edit his preset instead of creating one from scratch.
The snag I've hit is when I attempt to change the relevant sysex under the Custom Output column. I can get myself to the window that says BCR2000: Preset 1: Encoder 1: Line 1, which shows the sysex string broken down into ten columns. Then I'm clicking the button marked T (Edit All Output Items As a Single Line of Text). This opens yet another window called Output Statement. When I enter the sysex string for my JX10 parameter and hit the OK button I get this popup message: Error 10: Invalid numerical argument.
I'm guessing that this might be occurring because Rainer's sysex string contained 10 elements ( F0 41 36 0f 21 20 01 0B VAL F7 ) whereas the sysex string I'm trying to replace it with contains 11 ( A F0 41 39 00 24 20 01 0B VAL F7 ). The tone parameter sysex for my JX10 all begin with A or B to denote whether the parameter in question is for the Upper or Lower tone (not an issue with the JX8p).
I thought that perhaps adding an 11th column to the BCR2000: Preset 1: Encoder 1: Line 1 window's ten sysex columns might solve the issue, but when I attempt to do that by hitting the Insert New Item button I get a window called Custom output item 1, that has many options beyond my sysex knowledge to choose.
*Edit: I added an 11th column to the top of the ten, and set it to hex A (0A), but I still got the Error 10: Invalid numerical argument when trying to add my sysex string afterward.
Any advice/ideas welcome! Either way I'll be back at it tomorrow with fresh eyes.