How to make a character in Rimworld with specific stats?

I want to make a scenario, where two friends crash-landed on a frozen tundra planet. These two friends have specific skills, injuries and start with a very high and positive relationship.

Through the scenario editor I can choose starting items, research items etc, I can even choose the planet I start on, but I don't understand how do I edit the stats of the starting characters? Do I need to get into modding for that or is there already an interface for that?

The easiest way to do this is with the mod Prepare Carefully.

The above link has download locations, or the mod can be found on the Steam Workshop

The scenario editor does not allow you to create specific characters for a scenario. The main idea behind Rimworld scenarios is that with good planning, a player can "win" even with less-than-stellar starting pawns. Players can try to min-max their starting power by rerolling a bunch of times (or by using the Prepare Carefully mod, as Studoku mentions), but it should not be required to win.