It's definitely possible to do with save editing, the 'trailer_owned' chassis and model need to be replaced with the single model that is used by the company under the default 'trailer' folder. Any accessories might not be compatible with the model, and different trailer types can be specified and definitions edited independently from the model data. You can then apply the paintjob in \trailer\scs_box\curtain_sider\company_paint_job\scania_fac.sii
I did a quick swap with a custom trailer I had already, this was an insulated dry van but you can use any model you wish:
http://images.get-script.net/ets2_20210611_192529_00.png
Let me know if you want any help with making this on your profile ?