Co-operative Group will pilot a new convenience offer at 10 of the Alldays stores which it acquired in October.
The stores will be relaunched under the group's Welcome convenience fascia in late January and early February at a total cost of £1.6m.
A 2,700 sq ft store at North Baddesley in Southampton has been the first to undergo the redevelopment and will officially reopen on January 23.
New signage and shelving have been introduced and the store's emphasis will be on fresh produce, with a 500% increase in the fresh range. A spokeswoman said the Co-operative Group was combining its expertise in convenience grocery retailing with Alldays' strengths in CTN categories, and the trial would focus on enhancing the range and merchandising in CTN and fresh food categories.
The 12-week pilot will be evaluated before the group launches a multi-million pound refit for the rest of the Alldays estate. It said completion was due within three years.
"This is not just about changing the signs above the doors but about bringing out the strengths of both businesses and determining how we move forward as the UK's leading convenience retailer," said Malcolm Hepworth, chief operating officer, Co-operative Retail.