[FEATURE] Overridable Plan mode system prompt

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

From my understanding when you activate Plan mode it loads the built-in Plan mode system prompt. Just as one can override the default system prompt (with claude --system-prompt-file system.md). One might want to override such built-in system prompts (e.g. to disable the built-in Plan subagent that keeps wasting tokens).

• https://code.claude.com/docs/en/cli-reference#cli-flags

Proposed Solution

claude --plan-system-prompt-file plan.md

Alternative Solutions

Just found an alternative, tweakcc allows replacing all Claude Code system prompts:

• https://github.com/Piebald-AI/tweakcc

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

To disable the built-in Plan subagent that keeps wasting tokens when in Plan mode.

Additional Context

_No response_