Schools are being warned that they have a "moral responsibility" to keep the cost of uniforms down as they change status.
The Local Government Association (LGA) says families do not have an "endless pot of cash" to pay for new clothing as the recession squeezes household budgets.
Parents should not feel forced to buy expensive new uniforms because their child is going to a new free school or one that has "rebranded" as an academy, it said.
More than half of England's secondary schools have now converted to academy status, and the number of taxpayer-funded, self-governing "free schools" will reach 74 in September.
The LGA said schools that decide to alter their uniform should restrict changes to one or two items or to badges that can be sewn on to clothing.
The average school uniform now costs more than £200 for secondary pupils, or £160 for those in primary school, according to the organisation.
Sports and PE kit as well as other school items send costs spiralling higher.
Councillor David Simmonds, chair of the LGA's Children and Young People Board, said schools should offer their uniforms to multiple retailers and that parents should put pressure on schools to give them a fair deal.
He said: "In the current education landscape, dozens of schools across the country are changing their names or identities.
"It is understandable that many will want to mark this, but they need to remember that parents do not have an endless pot of cash for new school clothing.
"Headteachers have a moral responsibility to minimise any additional costs that occur because they change their name or status, for whatever reason."