This post shows you how to update all objects in a collection using Linq in C#.
For example:
foreach (var o in collection)
{
o.PropertyToSet = value;
}
If you want to use just the framework you can do
collection.Select(o => {o.PropertyToSet = value; return o;}).ToList();
The ToList is needed in order to evaluate the select immediately due to lazy evaluation.
Another way
collection.ToList().ForEach(o => o.PropertyToSet = value);