old two wire house adding new wire to existing runs

The correct answer is to file for a building permit and ask the local AHJ. But to answer your question, yes, clip the ground and use 2-pole receptacles without a grounding terminal. That being said, it would be far better to run a separate ground wire to the existing 2-pole receptcles, change them to 3-prong, and then continue the NM with ground on from there. The NEC reference is 250.130 Equipment Grounding Conductor Connections. ....... For replacement of nongrounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C). ....(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following: ..... (3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates (4) An· equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates (5) For grounded systems, the grounded service conductor within the service equipment enclosure (6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure