Then leave it as it is, with Northwich in Conference North next season. I agree with everyone else that they should not escape relegation.
Here is my proposal. Let the Conference Proper run next season with 21 clubs, and at the end of next season, the bottom three in the Conference go down as usual (*sarcasm!).
To replace them will be the winners of Conference North and South, who will be promoted automatically, plus the play off winners of both Conference North AND Conference South, hence providing the extra club.
At least that way everyone will know from the start where they stand.