Getting to Mars is hard and may take longer than we anticipate. Terraforming it in any meaningful way is going to be even harder and would take centuries. The challenges are outlined here.
Proponents of terraforming often focus on changing a planet’s environment to make it friendlier to humans and other forms of life as we know them today. If there is discussion of engineering microbes and plants to better survive in the harsh environment of another planet, the goal is typically still to use those engineered organisms to make the planet a friendlier place for us. An example would be the use of plants and cyanobacteria to make oxygen that can be breathed by humans.
An alternative approach that doesn’t come up as much would be to engineer life forms that can permanently survive in space and on other plants without the goal of altering those environments to suit humans. In Infinite in All Directions, Freeman Dyson writes this:
There are three principal obstacles to be overcome in adapting a terrestrial species to life in space. It must learn to live and be happy in zero-G, zero-T, and zero-P, that is to say, zero-gravity, zero-temperature, and zero-pressure.
He goes on to argue that low temperatures aren’t much of an obstacle to life, and that zero-P and zero-G are also solvable. While he talks about life in an abstract sense, for organic life as we know it, probably zero-water would be the hardest obstacle to overcome.
We have some knowledge about the adaptability of life on Earth, but we don’t know to what extent life could adapt to conditions off Earth. Finding this out sooner rather than later seems like a worthwhile research goal. Can we engineer organisms that can survive in permanently sub-freezing temperature? How about zero-G? How about zero-P? How about zero-P and zero-T and zero-G and with extremely little water and with high ionizing radiation?
Nehaveigur 