mautic:assets:generate is generally what may be needed if JS was changed.
GrapesJS is different, though, because not native Mautic… and can be pretty ugly (see GitHub - mautic/grapesjs-preset-mautic: GrapesJS preset configuration for the Mautic editor).
Therefore the recommended way for changes is to create a GrapesJS plugin, see GrapesJS Builder — Mautic Developer Documentation 3.0.0 documentation