You cannot “replace a few chips” to remove an iCloud lock nor can you reprogram these chips. If it was that easy, the market would be flooded with iCloud Unlocked devices and iPhone theft would be a rampant problem.
Apple has done it’s homework here and made iCloud Lock essentially impenetrable. The only known exception is when an internal Apple employee sells GSX access to unlock the device but that’s a different barrel of fish.
Essentially, the CPU/NAND/Baseband CPU and EEPROM are all tied together with a secure code. While you can reprogram the NAND, there is no such access to the CPU or Baseband CPU. Therefore, the only way to make a logic board unlocked is to transfer those IC’s from a non locked board…that’s a whole lot of work for nothing as you haven’t made anything new, you risk damaging both boards (this is a very difficult repair with low success rates) and it would have been easier to just transfer the unlocked board in the first place.
Unfortunately, in regards to iCloud locked boards, you can’t make something out of nothing.