This doesn't really pass the sniff test; if there were any easy one-gene changes that resulted in unambiguously better results, it's highly likely that we'd all have them already.
All that to say that, in these cases, sure _most_ people have positive traits from these genes, not all do and we could theoretically use CRISPR to change people with the negative versions of these genes to the positive versions of these genes.
[0]: https://www.nationalbreastcancer.org/what-is-brca [1]:https://www.alzheimersorganization.org/alzheimers-gene-apoe4