1. Can I delete a change to a vanilla object in an ESP? I accidentally changed a vanilla armor and now in the ESP it has the "changed record" asterisk mark. I don't want it. Can I not start over?

2. If I change the name of an armor, and another esp changes its gold value, will both changes be present or only the last loaded change is present?

1. Yes, though depending on how much you change it may not be easy. Click Data, select your mod and say Details. It will load a list of every single change you've made. Find the one in question and hit Delete, say 'Yes' to Do you want to ignore this record? Then when you save, it will not save that change, and upon next playing or loading the esp it will be reverted/undone.

2. I'm not sure. The records are held in different spots, so I believe both would have effect. But someone with more knowhow will have to say for sure.

armor records will definitely override the entire thing depending on last mod loaded.

overwrites generally happen at the Form ID level, so changes to subrecords will be ignored