As far as the screen goes, I presume that warrantee would only cover the original parts. The warrantee for the original parts would be in tact in that case, and

As far as the screen goes, I presume that warrantee would only cover the original parts. The warrantee for the original parts would be in tact in that case, and in your example, the original parts are functioning as intended. The case where replacement parts (or the replacement process itself) damaged the original product is a concern. I think it has to come down to a balance ultimately -- wherever you place the bar, companies and customers alike will find ways to abuse it, it'll just be easier for one group or the other. I think overall though we need to err towards giving more power to consumers for one reason: Both groups have a lever to protect themselves from damages, companies can raise the cost of or not offer warranties, and costumers can choose to not buy the products. However, there's always an inherent information imbalance in the direction of companies -- they know their product better than you do, they know what they cheaped out on, they might have exclusive access to replacement parts, or exclusive expertise for repairs. And this in general makes it much easier to abuse consumers.