the klostra cannon can ONLY fire at planets that have been scouted or visited by fleet/ships, so no it will NOT fire at it.
the quick way to make a mod for entrenchment & diplomacy (easiest to mod) is create a folder in the mods-entrenchment( or diplomacy) v 1.### (the highest number you have) and call it the name of the mod, then create the gameinfo folder for entity's and copy the entity's that you want to alter into the mod's gameinfo folder, then text the entitys with a tool like my textbin gui which is also in my modding utilities pack which even has a mod updater to update older mods to current, then edit the texted entity files to the way you want them, if you add new entity files then you will also need to add them to the entity.manifest for the mod( and I also created a simple manifest maker in the modding utilities pack) then test the mod with the dev.exe in the same folder as the sins & entrenchment & diplomacy exe if you have the expansions.
to mod vanilla sins you NEED to copy the ENTIRE sins folders from your sins porgram folder to the created mod folder, then text the files, edit the entity's you want to, then test in the sins dev.exe.
harpo