A systematic investigation of the thermodynamic and structural properties of Ar-n-HF clusters in the n=1 to 12 range and comparisons with the corresponding homogeneous Arn+1 reveal that Ar-n-HF clusters undergo mixing isomerizations. We present evidence that in some cases (n=5, 9, and 10) some isomerizations take place at extremely cold temperatures (T<1 K). We estimate the temperature dependence of the redshift for Ar-n-HF using a semiclassical stochastic method. We find that the classical redshift depends strongly on temperature and is affected by Ar-HF exchanges. A quantitative structural characterization of the walk allows us to detect the onset of several distinct types of isomerizations for the less stable clusters.