"Is it possible replace Face ID parts?"に関する回答I work on iPhones all the time and I stopped at the iPhone 10 and above because they're hardware and software secure/ booby trapped. First the earpiece and front facing camera/IR illuminator is booby trapped. Second the LCD has firmware that can be checked and modified during any software update. I've had more than one iPhone 10 malfunction after proper LCD replacement including loss of sound from the earpiece and/or loudspeaker, the phone refuses to turn off (goes through the motions but returns to the home screen), loss of Face ID. After the replacement LCD was installed the phone worked fine. After the software was updated the phone started having problems. The LCD was an aftermarket/non-Apple inc. LCD
"Possible SMC damage from liquid spill - needs a logic board?"に関する回答I repairing these systems. If the SMC was bad you would not even get a green light on the magsafe. You'll need a schematic diagram and the boardview (.brd) file to find the part location. You may need to clean the board and possibly have a shorted backlight fuse (Backlight issue). If the battery doesn't charge (green light) the issue is possibly the Intersil ISL6259A (CSI/CSO) or the diode connecting the adapter to the Intersil.
"Broken on off switch"に関する回答Here: http://www.ebay.ie/itm/252034935133?ssPa...
"Can I replace my keyboard with a backlit one?"に関する回答I'm a tech and yes it can. You'll need to replace the modular electronic assembly that connects the trackpad and keyboard as well as the non existent backlight film with the parts from the later model. I'll cost about $100