I would like to rework those two questions at some point to have this functionality built in, but the custom code from that earlier forum post ought to work for now.
The use of a hundred predefined list items is arbitrary. It just needs to be whatever the maximum number of regions you expect a respondent to highlight. As-is, that code will ignore the 101st, 102nd, etc regions. If you want to go higher than a hundred, you'll just need to add more items to the predefined list and update the "100" in the forum code.
The items of the predefined list don't need to have any text in them. That forum code just uses the lists as dummies to know how many regions were highlighted. This lack of optimization is something I would want to fix in a rework, but it's hopefully alright for now.
I believe the separator is currently defined on line 169 of Highlighting: Custom Ranges. Specifically, you're looking for this:
selectedSep = ', ';
If you have commas in the text that respondents can highlight, you'll need to replace that separator with something that respondents can't have potentially highlighted.