First of all, thanks for a great program!
Second, there is a feature that I think could improve the usability of Metamorphose. It would be really useful if the program allowed for a list of files to be passed in the command line. For instance, once could use a file manager to select some files and then pass that list to Metamorphose through the command line (similar to the interaction between Krusader and KRename). I guess/hope it shouldn't be too difficult to implement.