A note is fine. I think. I was wanting to avoid "charm".

@@ -16,0 +17 @@
+<s_inf>spoken to ward off misfortune</s_inf>
@@ -22 +22,0 @@
-<gloss g_type="expl">spoken to ward off misfortune</gloss>

I think "charm spoken to ward off misfortune" is an explanatory gloss whereas "spoken to ward off misfortune" is a usage note.

To me, "spoken to ward off misfortune" is a usage note, 
not an expl. A test I suggested on the mailing list: "(I 
think) an expl should be able to be used as a (wordy) 
stand-alone translation of the word, e.g. 'I like two-
person comedy acts' doesn't look too off as a 
translation of  '漫才が好き'"
That's just my suggestion, though.

Daijr, GG5, etc.
https://en.wikipedia.org/wiki/Knocking_on_wood

I think these spoken phrases are not really charms. To me it's really an explanatory gloss.

@@ -17 +16,0 @@
-<s_inf>charm to ward off lightning and misfortune</s_inf>
@@ -19,0 +19,2 @@
+<gloss>heaven forbid</gloss>
+<gloss>God help me</gloss>
@@ -20,0 +22 @@
+<gloss g_type="expl">spoken to ward off misfortune</gloss>

Having "charm..." as an expl rather than a note opens up 
for misunderstandings, I think (くわばらくわばら is not an 
omamori type of lucky charm)

@@ -16,0 +17 @@
+<s_inf>charm to ward off lightning and misfortune</s_inf>
@@ -20 +20,0 @@
-<gloss g_type="expl">charm to ward off lightning and misfortune</gloss>