Is there a way to add combat skills to a gnome in the starting settings? I know you can change things like woodcutting and stuff, but I'd like to give them some decent combat stats too.
Yes and no. You can improve you weapon skills but cant set your own numbers it is all randomly generated.
In order to do that it has to be attached to individuals starting professions not individual gnomes. Meaning all miners could be better at (what ever skill(s) you set) but others starting professions wouldn't be unless you added that skill to there starting profession aswell.
In order to achieve this in theory, I stress theory
this isn't something I have tried. You would have to edit the newgamesettings.xml.
You should see a long list of entries similar to this for each profession.
You will need to add what ever skills you would like within each of the professions you would like to be better at combat for example here I included NaturalAttack which improves fighting.
If your looking for a complete list of skills open up the skill.xml.
Given that you start the game with Miners, Farmers, Woodcutters, Builders and a Rancher. I would only try editing one of those professions at first to test it out but if it gives them a boost let me know.