assign value using linq

using Linq would be:

 listOfCompany.Where(c=> c.id == 1).FirstOrDefault().Name = "Whatever Name";

UPDATE

This can be simplified to be...

 listOfCompany.FirstOrDefault(c=> c.id == 1).Name = "Whatever Name";

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UPDATE

For multiple items (condition is met by multiple items):

 listOfCompany.Where(c=> c.id == 1).ToList().ForEach(cc => cc.Name = "Whatever Name");

You can create a extension method:

public static IEnumerable<T> Do<T>(this IEnumerable<T> self, Action<T> action) {
    foreach(var item in self) {
        action(item);
        yield return item;
    }
}

And then use it in code:

listofCompany.Do(d=>d.Id = 1);
listofCompany.Where(d=>d.Name.Contains("Inc")).Do(d=>d.Id = 1);