Upon loading Temporal Flux (during the TileEditor_plugins Constructor()), load the check _ifHasBeenModified, (display a 'warning msg box' since the tile editor has been loaded with a ROM that hasn't been 'fitted' yet). I can't imagine someone trying to load plugins after loading a ROM so this would be done at ROM load.
A check at ROM load isn't necessary. At ROM load, Temporal Flux loads all tile graphics from the ROM for the tileset editor. The decompressed data held by Temporal Flux is inaccessible to plugins, so a plugin would need to create a separate copy of of the decompressed data, and write the plugin's copy back to the ROM on save, which would not be shown in the map editor until a second ROM load.
That Plugin Architecture is what I reference for my plugins.
How can we make (easier) new plugins for ourselves?
For instances make a button that changes every Death Peak Music Track (to Singing Mountain), and edit/update the event files to use Singing Mountain rather than Silent Light. (ie. edit a string of commands and events files in Temporal Flux in one file or button.
A music change plugin like that would be difficult to create. Plugins can't access the loaded event data, which makes things difficult to mess with.