Using version control for module files often points out that diffing modules even on rough scale could be useful. Without being of aware of existing solutions, I wrote a little hack to OpenMPT with which it is possible to set e.g. TortoiseSVN to use mptrack.exe with appropriate command line arguments to do module diffs [1]. Attached is the code and an example what the module diff looks like. Comparison is based on as-simple-as-possible module-to-text conversion (currently highly lossy, but covers big parts such as pattern data) and use of existing diff programs for the actual comparison. Note that this is a demonstration-of-concept type of patch and is by no means intended to be merged as such, but can be improved if this type of functionality is of interest.
[1] Diffing works from TortoiseSVN context menu by adding the following as handler of it/mptm etc. extensions:
"C:\Program Files (x86)\OpenMPT\mptrackWithDiffFunctionality.exe" /diff "C:\Program Files\TortoiseSVN\bin\TortoiseMerge.exe" %base %mine
