The long-serving legend said goodbye in December 2020 after 14 years at the helm, taking the club from Step 5 to the National League North.
But a u-turn has been performed following the departures of Bernard Morley and Anthony Johnson.
Ainsley takes over until the end of the season with the club sitting in 16th in the table. Former Moors midfielder Jamie Chandler has been appointed as his assistant.
“We felt it was key to add a little more clarity to the football management structure and we’re delighted with the team we now have in place,” said Moors Chief Executive Brad Groves on the club’s website.
“In Jason we have someone who is vastly experienced in the role and who has previously brought great success to the club, so it’s fantastic seeing him back at the helm.
“Jamie Chandler has proven himself to be a very talented coach and we’re excited to see him continue to flourish in this new role working closely with Jason.
“Lewis will also add great knowledge and experience from a coaching point of view, so we offer him a very warm welcome back to The Brewery Field and wish him every success.
“James Curtis will now revert to his role as club captain and we want to thank him for his work and support over the past couple of weeks.
“We are confident that the management team we have installed now can help provide the improvements we need to meet our goals for the season.
“They are already working hard to identify targets who can improve our current squad and they will have further funds available to complete that strengthening as soon as possible.”