How to assign a glyph to a keyboard stroke in a best way?

Does @Peter Kahrel  code with '\uFB30' work? It does for me testing with the Arial Hebrew font

try {
    app.selection[0].contents = '\uFB30';
} catch (_) {
    alert ('Please select an insertion point');
}

Glyph IDs are font specific and only used when no other combination of character code and text attributes produces them.

E.g. when you insert the glyph via glyphs panel, InDesign will try its best to insert a real character set various attributes or toggle umpteen opentype settings for it (the mouse-over tip for that glyph will tell). Only if that fails, it produces a real glyph.

Back to the problem. The easiest way in UI is to use an otherwise unused character and find-change-glyphs it when you have entered all of them.

I first thought (as in: burnt an hour) entering the gid/cid using a script should also be possible along Peter's attempt, but then remembered the old script from the original InDesign team themselves that creates all glyphs for a range by using an import - was it tagged text? When I needed it, I wrote an experimental plugin that produces random glyphs for the current font (for testing that font) but that won't help here.

Scripted find change glyph along my UI suggestion should be a more modern way. Left as exercise for any takers.

Place this script in your Scripts folder (change x to the character you need):

try {
  app.selection[0].contents = 'x';
} catch (_) {
  // Fail silently
}

 then in the Keyboard Shortcut editor apply a shortcut key to that script.

Look, if there is not a specific key dedicated to the glyph.