There should be a place on the credit application that shows you how you can "opt out" with all of the Credit Repositories so that you won't get any more "pre-approved" applications. IF for some reason there is not, you can write to the Credit Bureau listed on the application as the source that they obtained your credit report from. That Credit Bureau should notify all of the Credit Repositories that you don't want any more "pre-approved" credit applications. Once you have done that, you will not receive any more "pre-approved" solicitations for credit.
I brokered credit reports for Trans Union through my two Credit Bureaus, and I can get you the exact information to "opt out" IF you are still unable to stop the "pre-approved" solicitations. Federal Law requires them to cease and desist once you request them to do so in writing.
As far as messing up your credit so they will quit sending you the "pre-approved" applications go, it would be to your detriment to do so. If your credit score drops you won't be able to obtain credit when you want it. It will also increase the rate of interest when you use your other credit card accounts. It would be a very bad move on your part. You shouldn't go to such an extreme measure before you try what I have suggested. IF you need any additional information, feel free to FReepmail me. :o)
you seem to know a lot about this subject. What is the average credit score?