Skills added during a conversation
The list of skills the agent picks from is part of the conversation's system prompt, which stays fixed so the provider's prompt cache keeps working. When a skill is installed, created or removed while a conversation is open (from the Skills Hub, hermes skills install in another terminal, a plugin, the curator, or the agent itself), your next message to the agent carries a short note naming the new skills with their descriptions and the removed ones. The note is sent once per change; the system prompt itself picks up the change at the next compaction. /reload-skills is not needed for this, it still refreshes the /skill-name slash commands.
From the official Hermes Agent documentation.