ok this is a bit convoluted, but should work in CHS:
go to the search and replace tab and you will create 3 entries in this order:
First, a regex one:
Next, a regex one:
for Replace put a single space
Lastly, a non regex (though shouldnt matter):
What this does: Changes the first two dashes (or underscores) into the word DASHSEP
Then Replaces all remaining dashes/underscores into spaces
Then puts back the first two dash/underscores with dashes (note that if the first two were an underscore they will change to dash).
You might still be better off learning to use a simple scripts with CHS because that would allow you to tweak things like this and do more complicated stuff.