I think FAYT was and is exclusively designed to be triggered by the keyboard, not by scripting. At least I didn't find a way to do it when I was skimming through the Opus manual.
But I do use it for other purposes. Although automatic file selection when entering a folder can be scripted via a Script Add-in (as this example created by Leo illustrates), selected files are lost when you click into a folder. Yet when FAYT's "Find mode" is set to "Keep highlights visible after field closes (Esc to clear)" and you type something that corresponds to certain files, the coloring within those file names remains remains permanent (even when you open files in that folder, etc) - until you hit the Escape button. Which is the reason why I use this to quickly see my "sidecar" files in any folder I open.
Explainer (just to illustrate my case properly) : What I call my "sidecar files" are text files with the same name as its original file (a movie file, music file, pdf, ebook, or whatever) except it has a specific "sidecar" extension. An example (with FAYT-selection on "sidecar") :

This is VERY convenient for me, as it gives visibility to these specific files (which I'm using instead of "descript.ion" files since a while) and this visibility largely remains in tact watever I do in those folders. These files are also close to their 'original' when the list is sorted alphabetically, and even whien I sort on modify date (because my Opus editor dialog always adapts their modify datetimestamp to be identical to its 'original') - but those are just marginal details. My point is about giving those specific files more permanent visibility. And it works great. It also shows matches in the scrollbar (when that option is set in the FAYT find mode).
Yet, the way I've implemented this in my script add-in, which is called whenever I enter a folder, is a little awkward:
DOpus.SendKey("s");DOpus.SendKey("i");DOpus.SendKey("d");DOpus.SendKey("e");
DOpus.SendKey("c");DOpus.SendKey("a");DOpus.SendKey("r");
Is there a way to open up this highlighting feature for scripting?
E.g. something like this:
var cmd = DOpus.Create.Command;
cmd.RunCommand('Select PATTERN="sidecarfile" HIGHLIGHT="#ff0000"');
Not to mention the more trivial possibility to tune it with additional keywords like "keep" (to keep the highlighting active) and "matches" (for showing the matches in the scrollbar). Or those could be made the same as for FAYT highlighting. Also, hiding the type field in this case would be great.
It's just an idea. I'm seeing a powerful mechanism which has only been given limited use in the FAYT scope.