since you are editing a vanilla npc in an existing sandbox cell, you can just type COC SolitudeBluePalace in the main menu by bringing up the console without loading any save game.
creating a "virgin" save would be using the above method, but have no plugins active, then save the file. quit, load the game with plugin active and load the untarnished save game. every time you re-test the new changes to your plug in, you must load the virgin save
you can't test stuff like AI packages with existing game saves because there is so much information in the save file that will alter or conflict with any changes you make on the fly with your plugin, so you must always load a clean save or COC a test cell
OK, let me repeat it back to you to see if I've got it....
1. Unload all plugins.
2. Start game, immediately coc solitudebluepalace, then what... Wait for starting sequence to finish, maybe ask Elisif a question, something like that, and save?
3. make (or re-load) my test mod, then see how it works.
OK, now what? How do I go about de-bugging this?