Logic boards are indeed expensive, and primary components are soldered directly to the logic board of portable computers. Opening your device absolutely does not void your warranty. Using a third-party part does not void your warranty, other than its application to the third-party component, or damage as the result of a non-AASP repair.

https://www.apple.com/legal/sales-support/terms/repair/Retail_Repair_US_Terms_Conditions.html