Specify that a skill cannot be invoked implicitly

I used to utilize custom prompts.

They are very useful because I can inject them explicitly only when I want to; I have full control over them.

Now custom prompts are deprecated and the Codex team suggests the use of skills (link1, link2):

Custom prompts are deprecated. Use skills for reusable instructions that Codex can invoke explicitly or implicitly.

But, as far as I know, skills may be invoked implicitly (link):

Implicit invocation: Codex can decide to use an available skill when your task matches the skill’s description.

Would skills really work in place of deprecated custom prompts? Is it possible to define skills which will never be invoked implicitly?