I've tried sooooooooo many things, I red every thread about it. I have no idea what values allow a player to attack things. If anyone knows, please tell me. I would even pay money for a mod that makes NPCs killable like in the beta.
It should be in the npctype file, I think. Like "baseType" : "friendlyguard", I guess you would just have to change that to something else.
I gave an answer to the same question some time ago: http://community.playstarbound.com/threads/the-stepping-stones-to-genocide.131849/#post-3141496 If you want a list of available damageTeams: http://starbounder.org/Modding:Lua/Starbound_Datatypes#teamType