[NTG-context] change register entry separator

Hi, any way to change register entry and subentry separator from "+" to something else? Preferably to kanji character, so I'm sure it will not appear in the text. Entries and subentries are autoflushed, so it can be really anything. Other way around: I substitute "+" with " PLUS " in index terms before writing into the index, but which command is reading the sorted index entries to change it back to "+" when typesetting the sorted index on pages? Thanks, Jano