Change one element in a row at a time with an uniform probability.

Hello! I want to change one element in a row of my matrix at a time with uniform probability. Currenty my matrix of [50*50] chooses one element at a time from a set of [0, 0.1, 0. 0.2, 0.3, 0.4] with an uniform probability. With the following code. But in this more than one element changes at a time which does not satisfy the above condition. How to satisfy changing one element at a time with an uniform probablility?

    % code
    value_set = [range];
    numvalues = 50;
    x_star = value_set(randi(numel(value_set), 1, numvalues));