§3 - Save Editing
Causing extreme lag or game crashes by save editing is not permitted.
(If the Game Moderation Management thinks that your modification is not fit for our servers or negatively impacts other people, you are liable to be banned until the modification has been removed.)
§5.1
* Mixing vehicle items - Using car parts on a truck, truck parts on a trailer or car parts on a trailer, and vice versa for each case.
* Too many trailers - Using a modified trailer combination with more than 3 parts for ETS2 or 6 parts for ATS will cause the server to kick you, regardless of location on the map.
So the answer to your question is Yes, it is allowed. There is no other rule that is implying that you cannot do this.