ok, I thought that a name with an underscore might turn the glyph into a ligature and influence caret behavior, but it doesn’t matter it seems.
However, it does make a difference if the glyph is built with a substitution of 1) tildecomb, 2) tilde or 3) asciitilde.
When type three G’s, followed by the three tildes, with the default paragraph composer, InDesign always splits up the resulting glyph in two parts, with a caret in the middle. And only 1) seems to survive the clipboard to MS Word. Doing the same with the world ready composer activated: 1) turns into a single whole glyph, 2) and 3) remain split in two halves.
When inserting the precomposed glyph from the InDesign Glyphs panel, when the ccmp substitution also covers 2) or 3), it will result in two split halves, even when the world ready composer is active.
Only when ccmp contains sub G tildecomb by G_tildecomb; and nothing else, the Glyphs panel insert one whole glyph.
In MS Word, a caret appears at the center of the glyph when G and asciitilde are typed directly from the keyboard. When the three tildes are inserted right after a G, (by typing out their Unicodes followed by Alt+X) both 2) tilde and 3) asciitilde result in a caret position at the right side of the glyph, as if there is a non-spacing character, and only 1) tildecomb results in a single whole glyph, without any caret position, just like in InDesign with the world ready composer, which in my opinion is the desired result.
Conclusion, my “works like a charm” wasn’t completely charming.
The substitution with tildecomb works best, and adding ccmp substitutions for the spacing tildes might result in unwanted and inconsistent behavior.
Input method InDesign: Glyphs panel; input method MS Word: type G0303 followed by Alt-X.
And the World Ready Composer should be default in InDesign, but that is old news.