Replace Field Contents under the Records menu.
Do a find for the records you wish to change, enter the field you wish to change...then go to that option under the Records menu. It gives you 3 options...To use the value of the field/record you are on, a serial value, or use a formula to determine the value to use.
Try Replace Field Contents--using the calculation option.
You can store your expiration date and "person requesting" data in variables and refer to them in your replace field contents' calculation.
This enables you to enter data into a specified field for all the records in your current found set.
Since Replace field contents can modify large numbers of records in one go, it's a good idea to make a back up copy just before doing this until you are through testing your script and are confident it will work.
Also, Replace Field contents shouldn't be used in this manner if you have multiple users currently accessing the data base and possibly editing these same records as they can lock a record so that replace field contents fails to update that locked record. Run this script only under circumstances when this is not a possible situation.