Yes, some modifications could affect your vehicle's registration class.
Have you already made modifications to your truck?
Yeah, I'm in the process of modifying the exterior of my truck.
In this case, you will need to get a vehicle weight slip. These can be obtained at the majority of vehicle and metal scrapyards.
regarding DMV registration Could you provide me with a list of what I'll need to carry to the DMV to register a moped?
Firstly you will need to complete a Registration/Title Application form PDF (4) MV-82
Do you know  if I made modifications on my truck, will it affect the class of my truck?
Your vehicle can remain in the passenger class if it meets certain criteria and unladen weight requirements.
Does your truck have an unladen weight of less than 6,001 lbs.?
No, my truck weighs more than that.
Unfortunately, no relevant information is found.
Does this mean that I can't register it in the passenger class?
Although your truck weighs more than 6,000 lbs, you can still register it in the passenger class, if it's not being used exclusively for commercial purposes, does display any business ads, has a camper top that has one or more side windows completely enclosed, and has seats, seat fittings, and/or camping equipment installed in the bed.
Thanks for the information. What about cars? How can I register it from the passenger class to the commercial class?
Cars can be registered in the commercial class, if all seats are removed behind the driver and replaced with a permanent box or permanent rack to carry cargo.
Is there anywhere else I can obtain a weight slip for my truck?
Yes. Aside from vehicle and metal scrapyards, you can also receive a weight slip from some auto parts stores and mechanic shops, especially if they specialize in modifications.
How do I go about getting my car registered in the commercial class?