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I agree about having a small balance report on 1 card only. But not obtaining a SSL to replace any paid off loans. They may affect FICO 8 scores more harshly, but not the mortgage scores nearly as much. I think it would be more harmful to take a hard pull inquiry, new account, reduction of Youngest age of account, Average Age of accounts.
If you were just in general rebuilding credit, or keeping up scores with no big apps like a mortgage or auto, it would be fine. But seeking credit right as you plan to app is not a wise move, IMO.