A command set's commands are fixed in its manifest

Symptom

Your extension already loads most of its logic from a CDN, so changes ship without touching the package. Then a new toolbar action is requested — and there is no way to make it appear. There is no command to look up with tryGetCommand, and nothing you do at runtime creates one.

Cause

The commands are declared statically:

"items": {
  "OPEN_TOOLS": {
    "title": { "default": "Tools" },
    "iconImageUrl": "https://cdn.contoso.com/tools/icon.svg",
    "type": "command"
  }
}

The SPFx reference for the Command class says so directly: commands "are initially defined in the extension's manifest file"; at runtime you get the matching object from tryGetCommand and customize its appearance by assigning its properties.

Fix

Choose the shape before the first release:

• One entry, your own menu. A single command that opens a popover your code renders. Every future action is then data, not manifest — and your own menu can have submenus and group labels, which a command set cannot add to the SharePoint command bar or context menu.
• Reserved slots. Declare a few extra commands (SLOT_A, SLOT_B), keep them hidden (visible = false) until runtime configuration switches them on, and let the configuration supply their title and icon. Mind what Microsoft says about title: it is meant for minor changes such as "Submit these 3 items", because administrators are expected to understand what an extension does by reading its manifest. A slot stretches that intent — the manifest can only say that the slot exists, not what it will do — so give it an honest, generic title and tell admins that its actions come from configuration.

Notes

• After you change visible outside onListViewUpdated, call raiseOnChange() — it re-reads the property but does not re-run onListViewUpdated. Command set button never appears has the details, and the registration trap.
• The same holds for everything else the package carries: a new API permission request or a changed component manifest also needs a new .sppkg.
• Command class (SPFx reference)