Since the home button’s touch ID is paired to the logic board, you cannot change it and expect the button to function as touch ID any more. It will work as a plain home button though. The initial question had to do with the home button being cracked, not the flex cable. In order to answer the question, you have to take a look at the question the way it was asked. [br]
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I repair iPhones on a regular basis. I see all forms of issues with these phones. If the crack is not interfering with anything, I would not change it, especially if it is just an aesthetics issue. The other alternative is to locate a logic board with a matching home button. That can generally be gotten relatively inexpensively by going to eBay and finding a phone 8 with a broken screen that is for sale. Then it would just take someone like me or another repair tech that knows how to change it out, to swap the screen over to the other phone. Hopefully, you have all your data, photos, etc., backed up to iCloud. There is no other way to keep the fingerprint reader alive. If you don’t mind putting in a pin code to open the phone, you can just have the button replaced and be off and running. That would be the least expensive way to effect the repair.