If you have a hard threshold you want to use, then rmoutliers is not the function you want. Just use a simple logical index to get the location of the outliers, then you can do what you want with them.
locs = abs(y)>=1.2;
% locs = find(abs(y)>=1.2); % if having the indices is easier than a logical index
You can chose whether to remove those data points, set them to the threshold value, etc.
