This kind of thing (having a token rather than a single verb word as the first element of an ‘Understand [token] … as …ing’ phrase) is discouraged because although it sort of works under some circumstances, this so-called ‘verbless grammar’ isn’t fully and properly implemented- which is why the compiler doesn’t allow you to write ‘Understand “frotz/frotzify [something]” as frotzing.’
See here for more detail.
EDIT: The bug in 9.3/6M62 that led to incorrect assignment of topic snippets after commands such as ‘Darcy, hello’ when a story included any verbless grammar has been fixed in 10.1.2, but other issues persist.