I did this over a decade ago and it's still working. If I remember correctly I had to call to make it a permanent opt-out but it was totally worth it. My credit score was totally unaffected.

Essentially the same scenario with free credit reports and AnnualCreditReport.com. Just look up the instructions through ftc.gov whenever you're unsure about something. I still follow the link to the credit report site from ftc.gov these days even though I remember the actual .com as well, just for good measure.