The changes are part of the the 350,000-member National Trust for Scotland's strategy to increase visitor numbers and membership and generate more income as well as reduce running costs by 10 per cent.
The trust cares for 129 properties, with 70 gardens and designed landscapes. Over the next three years a £17m investment programme will benefit properties including Culzean Castle and Country Park in Ayrshire, Brodie Castle near Forres and Newhailes House in Musselburgh.
Major restructuring will affect many staff positions.There will be an overall cut in staff numbers, mainly at the trust's headquarters in Edinburgh, with 142 posts classified as 'at risk'.
Prospect, the trust's recognised trade union, said the redundancies would be a "devastating blow" to Scotland's heritage sector.
Only core services operating at national level will remain in Edinburgh; many decision-making, planning and conservation roles will be devolved to properties at regional and local levels.
Around 42 posts currently in Edinburgh will be transferred to be based alongside properties, while a total of 68 new posts will be created in areas such as commercial management.
Prospect has welcomed the commitment not to cut jobs at property locations, but fears the removal of vital central functions will lead to difficulties for members at trust properties.
Prospect negotiator Ian Perth said: "Our members are already significantly stretched and continue to do valuable work for the charity in such difficult times.
"We are concerned that the trust’s proposals rely heavily on replacing full-time staff with contractors. Although a move like this can show short-term cost reductions, they risk damaging the trust in the long-term."
Chief executive Simon Skinner, who has spearheaded the changes, said: "While the trust has achieved stability in the last few years, we have choices to make if we are to move forward and face up to ensuring our heritage remains relevant and engaging in an era of ever-more demanding, digitally-savvy generations.
"We need a step-change if we are to find and generate the investment we need to ensure the trust is fit for the future and offer world-class visitor experiences that are stimulating, thought-provoking and fun. Our core purposes are to promote access, engagement and learning , and we will begin by tempting visitors back to our properties in numbers that were last seen eight to 10 years ago."
The changes would save around £4m per year which will be reinvested in properties and modernising systems, Skinner added.
Affected staff would be able to take voluntary redundancy and as many people as possible would be matched to new posts to minimise compulsory redundancy, he said.
"But, inevitably, we will be losing some of our old friends and colleagues and some will have to move from their current base: change is not easy but change we must if we are to continue to deliver on our core purposes."
Prospect has 90 days to respond to the consultation.