But the Department of Conservation (Doc) says the changes have wide support and it has to consider health and safety issues.
Observation Rock is a short walk from the town of Oban and gives views of Paterson Inlet.
The track to the rock was renamed the Queen Elizabeth II Platinum Jubilee Path earlier this year by Prime Minister Jacinda Ardern.
Stewart Island resident Sharon Pasco said proposals to change the viewing place at Observation Rock had previously been put forward but had always been quashed as it was not wanted or needed.
The island’s greatest point of difference was its natural beauty and lack of man-made structures. But Doc would destroy that by constructing a viewing platform instead of the natural grass, she said.
"It seems ludicrous that we are trying to promote the island’s natural beauty yet we are going to do away with one of the most iconic sites on Stewart Island," she said.
"For all the day visitors it is a great place to see all the natural beauty of the island."
She said the viewing platform would be a barrier for many wheelchair users who could easily get to the viewing point now.
Many local residents had questioned the changes. A petition had been launched and a protest was planned on Monday at a Doc drop-in day over the proposal.
Doc senior ranger Dale Chittenden said the changes were proposed about 2018 and key stakeholders had formed a group shortly after that to progress the idea. It was based on a desire to promote the island’s dark skies sanctuary.
He said the proposal had been widely consulted on. Stakeholders included the Stewart Island Community Board, the Stewart Island Promotions Group and Great South.
"We are trying to make it as sympathetic to the environment as possible and have done a lot of consultation around this. We are not going to hinder the view."
Wheelchair users would be able to still access the view.
The drop-in session on Monday would help address any concerns.
The project would cost about $180,000, with funding by Doc, the island’s visitor levy fund and MBIE.
"Doc has to take on its legal responsibilities with health and safety and ensure to make it safe for visitors."
