I know both Darkness and Deep Shadows BFCs expressly forbid perplexing range above 6. They also limit powers/abilities to range of 6 (TK, OW, PC, etc). Does this mean that ICWO, as a feat (and not a power/ability), is permitted to increase range to 7? I am about to face a Nova Blaster in Deep Shadows and don't want to catch a nasty surprise

Technically, there is nothing to prevent you from doing this, no. However, I know that if you ever tried to do this at at one of my tournaments, you'd get a big, "Nice try, but no way, monkey boy!"

("monkey boy" totally optional )

I'd go for the timeless classic:
"Don't be a dink"

Deep Shadows, it specifically states that range value is limited to 6 and that perplex may not be used to increase it. In this case, I would say ICwO could be used to increase the range to 7.

Darkness, well, says darn near the same thing.

Now that I think about it, this is a darn good question. I think the good ole RA may need to rule on this.

It's really a matter of letter vs intent - according to the letter of the cards, it is legal, but it breaks the intent of the BFCs, which is why I would not allow it.