Re: Can i add a new attachment to an object without checking out and checking back in?
As Ben Loosli said in his reply, iteration is needed for the trace-ability and it is very core functionality of Windchill.
If you are looking for less no.of clicks for users to replace the file you can use: <Document> #Actions #Replace Action. This will replace the attachment in single click. This action will take care of both check-out and check-in automatically.