How can I modify specific key values within a dataset?

Question

Given a dataset, is there a way to modify a value?

Example

(*data = First@Import["dataset.xlsx"];*)
 data= {{"Supplier", "Material", "Geography", "Quantity"}, {"Acme", "A", 
  "United States", 676.}, {"Acme", "B", "Argentina", 520.}, {"Acme", 
  "C", "Russia", 186.}, {"Acme", "D", "France", 568.}, {"Acme", "E", 
  "United States", 201.}, {"Beta", "A", "Argentina", 483.}, {"Beta", 
  "D", "Russia", 289.}, {"Beta", "F", "France", 177.}, {"Beta", "G", 
  "United States", 169.}, {"Beta", "H", "Argentina", 842.}, {"Gamma", 
  "G", "Russia", 123.}, {"Gamma", "H", "France", 709.}, {"Gamma", "I",
   "United States", 579.}, {"Gamma", "J", "Argentina", 
  163.}, {"Gamma", "K", "Russia", 238.}, {"Delta", "A", "France", 
  405.}, {"Delta", "B", "United States", 411.}, {"Delta", "D", 
  "Argentina", 740.}, {"Delta", "H", "Russia", 322.}, {"Delta", "K", 
  "France", 321.}}

{fields, data} = {First[#], Rest[#]} &@data;
myDataset = 
  Dataset[Map[
    Association, (Rule[#[[1]], #[[2]]] & /@ Transpose[{fields, #}] & /@
       data)]];

Trying to update a value

myDataset[1, "Material"] = B

You'll get an error

Set::write: Tag Dataset in xxx [1,Material] is Protected.

Answer 1

This problem has already been discussed in this question. Taliesin Beynon said

As for when L-value assignment will be available, I'm hoping 10.0.1 or 10.0.2, which are in the next month or two.