Assuming you have a cell array of strings (much bigger than this simple example):
import = {'a1','a2';'a2','a4'};
Then you can replace 100 values with normally distributed random numbers as follows (obviously you will want to replace constants etc with the values you need):
newMatrix = zeros(size(import));
% generate 100 random numbers:
mean = 123.45;
stdDev = 21.0;
N = 100;
randVals = randn(1,N) * stdDev + mean;
for ii=1:N
indx = find(ismember(import, sprintf('a%d',ii)));
newMatrix(indx) = randVals(ii);
end
The new values will be in the matrix newMatrix
This is not super efficient; but it may be a start, and it may get other answers flowing (if you can confirm that this does indeed do what you intend - still not 100% sure I understand your question).