To have DITA2Go treat commas in DITA index entries as regular characters instead of index level separators, specify the following option:
[HelpOptions] ; IdxColon = No (default, allow colon and comma as level delimiters) ; or Yes (use only colon as delimiter, treat comma as regular text) IdxColon=Yes
You must also edit the WinHelp project file, yourdoc.hpj, to specify this option:
[OPTIONS] INDEX_SEPARATORS=":"