Not that I know of - also, it's not a 1:1 process - MT-32 has many more variations of e.g. strings or pianos than General MIDI does. But I could probably relatively quickly do a simple command line tool that takes a MIDI input file and outputs a remapped file, based on a text list of mappings. I.e., a text list like:
1 : 5 # remap (MT-32) instrument 1 to (GM) instrument 5
2 : 4 # remap (MT-32) instrument 2 to (GM) instrument 4
3 : 3
5 : 2
...
126 : 81
127 : 86
SCUMMRev 1 did it (it's what we used as a basis for conversion of HighLand MIDIs) - but SCUMMRev 1 hasn't existed for almost 25 years. 🙂