You can use an escalation to call an external script that uses mrSetField.pl to set a field value.
On my server I created a folder called scripts in the Fooptints\CGI directory.
In your escalation call your script like so:
C:\FootPrints\cgi\Scripts\Batch\SCRIPTNAME.bat %%MRID%% %%PROJID%%
Use the following line in your batch file to set a fields value. To zero the field, don't put anything between the value quotes.
Start c:\FootPrints\bin\Perl\bin\perl.exe c:\FootPrints\bin\mrSetField.pl %1 "FIELDNAME" "VALUE" %2