If so, open the model in v5.2 and save as a .m file. Then run the generated .m file under MATLAB while connected to a v5.0 COMSOL Server. Finally use the mphsave() function in MATLAB to save an mph file (that should be compatible with v5.0).
Note that when you run the .m file you may need to adjust some variable and tag names if you get errors. These can change between versions of COMSOL. Good luck!