Delete content in a user registration field after X number of days I am looking for a way to delete the data in a custom registration field (field:transaction_code) after 30 days. How can this be achieved?

Let me explain better. I want users to get the registration code from me. When they have that registration code, their accounts will be valid for 30 days. Once those 30 days are over, the user will then be required to enter a new transaction code. Thus they will need to revisit the registration page
Are you sure this is the right way to proceed? 
I think it would be better if you use a custom field with 2 properties: the registration code and a timestamp which holds the time until the value is valid.

And every time when you want to use the value, you check the timestamp. Also with this version you could easily set up a cron or advancedqueue job to delete old values.