The time when we will be able to modify vertebrates to thrive in microgravity is much farther in the future than the time when we will be able to build interplanetary ships with artificial gravity generated by rotation.

The former requires some scientific breakthroughs for which it is unpredictable when they will happen.

The latter is an engineering problem with very little unknowns, which is guaranteed to be solvable today if enough money are provided for it.

Until now, the additional costs for rotating ships could be avoided, as long as humans did not go farther away than the Moon.

For an expedition to Mars or even to some more distant celestial body, currently there is no known way that would avoid severe health damage for the humans, without using artificial gravity.

The experiments on the ISS have shown that for mice a gravity of at least 2/3 of that of Earth is required to completely avoid all health problems, while a gravity of at least 1/3 of that of Earth is necessary to avoid the most dangerous health problems.

It is unlikely that humans will prove to be much more resilient than mice.

Ont should start rightaway exactly because it's so faraway. I'm also comparing to all the materials research that are being suggested here, for which breakthroughs seem ... quite impossible?

And out there, you have free radiation for that accelerated evolution..