I must stick up for "replacize"! I think it's the very best thing in the script. Yes, "replace" is better English, but that would make "replaceFile" misleading — it's not the file that's being replaced at all, but regex matches within the file. To get clarity you'd need something like "replaceMatchesInFile", and that is quite a bit longer. Moreover, it's generic. When your program has a specific and unique technical concept, it's better to give that concept a specific and unique name and use that name consistently everywhere. (Best of all is when the name is lexically unique so you can grep it to obtain every single instance of the concept in your program. That property is so valuable that it deserves to have an essay written about it.) Generic English words are not always an advantage in code. As a program grows, they're likely to appear in more and more (unrelated) places, which makes them less and less valuable for conveying the program's key semantics.
"Replacize" is one of a zillion ways to get the desired effect, but it does it well and with style, and I like it. More than that, it's the one thing in the script that gives it conceptual unity. If you highlight "replacize" in your browser and jump between the various occurrences, the structure of the program immediately leaps out.
This kind of terminological pidgin, unique to a given program, can be very helpful in making code clear without making it verbose. The trick is to make sure that each such term has exactly one well-defined meaning and that it's used consistently everywhere that it applies. Eric Evans has called this the "ubiquitous language" of a program. The current script is tiny, of course, but if I see a programmer taking that degree of care with their writing anywhere, it's a stroke in their favor.
The thing in there that makes my eyes water, if not bleed, is the unfortunate duplication between the async and sync versions of the logic. But that is hardly the script's fault. It would have to be rectified at the level of the language and/or platform; little can be done about it in a program like this. Error handling too.