Having thought about this for a while, I think a moderately safe thing to do (when it is actually possible to control the biological outcomes with some vague notion as to the actually likely long term phenotypic results) is to offer financial subsidies to help improve the future generations of those least well off in the current regime, especially for any of a large list of pro-social improvements (that parents get to choose between and will hopefully choose in different ways to prevent a monoculture).

Also, figuring out the phenotypic results is likely to involve mistakes that cost entire human lives in forgone potential, and there should probably be a way to protect against this downside in advance, like with bonds/insurance purchased prior to birth to make sure we have budgeted to properly care for people who might have been amazing but turned out to be slightly handicapped.