Update .dat parameter file during the run-time

Hi,

I have a scenario in the load test where i need to fetch a token and pass has a header in the subsequent request. The token is valid for 24hours. So while running the load test vuser1 should fetch token using the credentials taken from the parameter file and should update the same parameter file with new token. So that vuser02 will check the tokenvalidity and if valid it should use that token directly, not fetching again. Any suggestions how to write/update the data in the parameter file during run-time so that it can be used by other virtual users also?

Regards,

Diresh