I think you can use it. If you check truckersmp rules it says "Negative cargo mass - Using a trailer with a mass lower than 0" is forbidden but I think it's okay if you decrease it to 1 ton.
Also you can check save editing rules:
"Causing extreme lag or game crashes by save editing is not permitted. Extreme lag will not occur from duplicate parts unless the amount is truly excessive. If you save edit to create a very long trailer combination but cannot safely handle it, you are liable to be banned for reckless driving / blocking and recommended to remove the particular mod. If the Game Moderation Management thinks that your modification is not fit for our servers or negatively impact other people, you are liable to be banned until the modification has been removed."