This sounds like a rather sophisticated way of constructing output. I'm not sure if that is easily acomplished with the "to file" block. I like to use S-functions to control my output.
In fact, I have an S-function that is the first block to run in my model (this is accomplished by placing it at the top level of the model and assigning it a priority = 1). this block reads a number from a file called "serialNumber", increments the number, and saves the incremented number bask to the "serialNumber" file. This serial number is used in other S-functions that generate output files, and appended to the output file name, so that every time I run the model the output is recorded in a new file with a "run number" attached to the file name. I can keep a log of all of the runs (date, time, run parameters), and pull up results for comparison (by run number) later. In fact, you can have the S-function that reads the serial number keep the run log in a file for you.