Hi,
there is no easy way to do this, but you can run the MZero and MSHE toolbox utilities from a batch file.
So, you could set up a batch file to
1. Mzero/TxStat: extract all the seasonal values one after another to separate dfs2 files (one for each season)
2. MSHE/Grid Calculator: add the dfs2 output files together and divide by the number of files
The other way to do this is to use the Software Development Kit APIs to write a short program to read the output files and write a new file.
Regards,
Douglas