Change a site's hosting plan (upgrade or downgrade).
Requires: API key with admin scope. Best practice: create a snapshot
before downgrading.
Args:
slug: Site identifier
new_plan: Target plan slug (e.g. "site_pro", "site_managed").
Call list_plans() to see available plans.
Returns:
{"success": true, "old_plan": "site_starter", "new_plan": "site_pro",
"message": "Plan changed successfully"}
Errors:
NOT_FOUND: Unknown slug
VALIDATION_ERROR: Invalid plan slug or same plan