Is it possible to have NPC's use the "combat dummy" and the "archery target" as if they are idle markers?
I know I can make a package to do this, but I'd rather the NPC's use them as one of their options while sanboxing instead of having to pick specific times in their schedule
I looked for something like this for a while and gave up. There is no asset in vanilla that allows idle dummy practice. You might be able to make your own idle marker that uses the combat animations and force some other things through scripting (might be required for archery practice to get the arrows to fly).
You COULD create the AI procedure to practice combat to happen as part of a larger sandbox procedure rather than giving it a specific time.