BCGControlBar Pro for MFC
UINT BCGM_ON_RIBBON_CUSTOMIZE

The message is sent to parent frame when user begins customization.

Parameters
wParamThis parameter is not used.
lParamA pointer to ribbon control to be customized.
Returns
Application should return nonzero if it processes this message and displays its own customization dialog. Otherwise the library will display built-in customization dialog.

You should process this message if you wish to display your own customization dialog.