It would be useful to have some method to have a host or hostgroup override that would remove an array value. I'm initially thinking about a packages parameter that manages software on a computer. I'm thinking something like where the default array might be ["package1","package2","package3"] but a hostgroup or host could merge ["package4","-package1"] so the resulting array sent to puppet via ENC would be ["package2","package3","package4"]. Here I use the leading - as seen in globbing lists like in duply or other projects as an easy to use syntax, though I suppose there might be a package that started with the "-" character so a different syntax might be {"package4":{"ensure": "present"},{"package1":{"ensure": "absent"}}, though how you would know that's referring to the array values is not clear to me either.