Enable an actual closure to be passed to CliHelper apply-closures

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

This feature enables commands extending nodes:update to pass real closures rather than strings.