Replacing a socketed component that is modular by design, even if it's not officially intended to be upgraded outside the factory, is worlds different from replacing BGA components on a densely packed PCB.
That said, there could also be a middle ground by just providing some way to look up the hardware specs of a given serial number. Post the part numbers of the components that you're concerned about being replaced and provide tools to verify as many of them through software as is practical. Allow owners to know if their device has been modified and how so, but allow them to choose what to do with that information.
Combating fraudsters trying to pass off modified and/or refurbished devices as genuine is valid, but preventing owners from modifying or repairing their own or knowingly purchasing such devices from honest resellers is not.
I'm sorry, you seem to be confused. Soldering is not the problem. Locking up the hardware to have hardware provisioned tier limits to block you from upgrading your own hardware is silly.
And do note, raspberry pi doesn't prevent you from switching RAM chips. The board will continue to work just the same with high capacity variants. But for some reason raspberry pi hardcodes a max memory size that prevents you from using the hardware upgrade you paid for in full.