Please don't kill feeders with hammers. It's NOT humane. You say you had rat pets in the past and enjoyed them in the same thread you describe smashing one in the skull to kill it - this does not compute with me. You shouldn't be buying a live animal to feed your pet if you don't have the ability/resources to a) kill it humanely b) house, feed, and water it.
Place something rigid like a spoon handle or some kind of rod behind the ears on the back of the skull and pin it to a table at the same time you give a very firm tug on the base of the tail. There are plenty of videos and tutorials around the internet - it's called cervical dislocation.
As for the snake struggling a bit to get the rat positioned to rat it - it's because you let the rat reach the state of rigor mortis before freezing it. Once it's dead you should freeze it right away directly to the freezer. When you thaw it out it should be limp like it was when you first killed it. Like this, there shouldn't be a difference between a rat that the snake killed themself and the one you thawed out. Another possibility is your thawing method - it should be thawed in open air and heated just prior to offering. People who overheat or try to thaw rapidly using heat often talk about exploding bodies, excess blood, etc. This is because the cells are not meant to freeze and thaw rapidly and sustain too much damage through that process to hold integrity.
If F/T is not for you - get a tank, water bottle, food, and treat your feeders like a pet until you're ready to offer again. You have a baby growing inside you and can smash another mammal with a hammer without an ounce of compassion - another contradiction that boggles me. Did you know rats are 80+% genetically identical to humans?