I worked in the industry and your credit score was the primary reason we based off your rate, and we knocked it down a bit if there was a promo or if you had autopay.
You don't get dinged hard by just applying. Ask how long they keep your credit report before pulling it again and just get rate quotes during that time period. It's smart and also lenders know when they'll be increasing rates before it goes in affect so it doesn't hurt to do it now and then just wade it out.
Also ask for a rate modification. Nobody knows about this but you can request to get just your rate modified and nothing else changes. It's WAY less time consuming, cheaper, you don't need an appraisal, and can be done in a day. The downside is you can't get "new money" (more than your current principle balance) and you're not extending your loan.
On a different note, 2% default != 2% loss. Mortgages are secured by the property, losing investors only a small fraction in foreclosure, so a 2% default * 25% severity = 0.5% loss.
For the same reason, I expect margin interest to drop by the same amount.