How often should a home care plan be done if there are no changes in client’s condition?

Usually care plans are assessed quarterly, even if the conclusion is "no changes".

I can’t hazard a guess without more info.
Who is receiving the care? Who is providing the care?

How do you know there are no changes? Have you been the caregiver for the client since the last care plan?

Is someone expecting the results? Is someone using the results in order to keep abreast of the clients condition.

It seems a prudent practice to have a regular care plan and to update it officially on a periodic basis but w/o more information not sure how to help you with your question.