It’s one of the possible lab finales. In older versions, you can only use the CVD machine on a handful of weapons, and you also needed a certain book for the recipes. Now it’s kinda more convenient, as any cutting weapon (I think it needs a certain amount of cutting damage to qualify) can be diamond-coated. Sadly, that meant that diamond rapiers are no longer possible since they use piercing damage.
Anyway, most combat skills can go beyond ten. Like, from constant fighting (60,000+ kills so far and no chance of stopping), my survivor has 17 in marksmanship, 16 in rifles, 15 in SMGs, 12 in handguns, 9 in launchers and shotguns, and 13 dodge.
Survivor still gets damaged, though she’s pretty encumbered in some areas. Like -4 in dodge due to torso and leg encumbrance.
In comparison, her close combat skills aren’t as high, since it seems to take longer to train them. Around 9 at the highest and 6 at the lowest.