I just call it creation. To create a TAS.
Haven't used the term "write" there, because it too much points towards book-like pursuits, and while both are creative pursuits, involving rules, goals, and designing, you wouldn't call painting, which is also a creative work, by "to write a painting".
Then again, I am not opposed to using the word "playing" in this context. After all, when TASVideos was young, I intentionally emphasized in my propaga
^H^H^H^H^H^H^HFAQ materials, how TAS-players are really playing the game normally, with tools that enable them to play at high precision, to dispel the myth that TASing involves video editing, hacking the games, or is fake and cheating.
Today, I even like to say that TASing is simply just regular speedrunning, except with arbitrary segmentation. There is a really narrow line between those two. I consider segmented speedruns as TASes (when speaking to people already familiar with both concepts).
True, there are more tools that are widespread today, such as RAM watching and robots, but using robots (scripts) is not new in RTA speedrun communities either.
Perhaps the most fundamental difference arises from our site rules: All TASes must be reproducable in the form of an input stream that can be fed to the unmodified game, possibly running under an emulator to accomplish it.
But it's not like I haven't
broken that rule either. And, it's not like RTAs have not been
produced that also provide an input file.
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^H was used here for epanorthosis. Unfamiliar, too young to remember? http://en.wikipedia.org/wiki/Backspace#.5EH may help.