Try creating a copy of the sniper beam file, place it in a directory outside the legions folder.
Delete the purple sniper beam file from your legions folder, and update the legions patcher.
Although you may not be able to update your legions patcher at all, if you have any other mod's set read-only.
If you can find a way around that, either by deleting your legions live folder completely, and then updating the patcher. You could also create a copy file of all the other mods you have in your legions folder, you can always replace them later on.
After you update the patcher, replace the original sniper beam with your edited (green one) directly, try not to replace the original with an un-edited version and then try to edit it in the legions folder.