With the mind blanking and restoring, one assumes that they know how to copy your brain into another body. So why not one where any old man gets a new body it’s younger and he fucks his granddaughter or his granddaughter‘s friend

They don’t really copy memories. It’s more that they create fugue states and alternate personalities. They bring up the “original” when one is deblanked.

Also, I wouldn’t do granddaughters (even mental transplants), because I don’t do genetically related smut. However, there are authors around who are up for that and I hope you can connect with them. Maybe one will spot this post :)

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Edit/Update based on missing part of the question: The old man wouldn’t need a younger body to fuck the granddaughter’s friend. He’d just have her blanked and conditioned to love his old, wrinkly body. ;)