rick c:

The dealer probably could not be cited by OSHA for such a violation. It could trigger, however, an OSHA inspection of the dealer's facilities. Such activity by the dealer always leaves the possibility of civil action by the employer who may be cited.

Where the "safe operation" starts and stops is a gray area. When in doubt go with the manufacturer's written authorization.

Using a certified welder may not be sufficient. Can the welder determine how much of a weld is necessary for the maximum forces that could be imposed on the load backrest extension? Do the bolts you use as replacement meet the tensile strength set by the manufacturer? Are the bolts cheap knock-offs? These are the questions that must be asked where life or death is involved.

One of the concepts of risk management is to pass the risk on to others where possible. In your case it may cause some delay and extra cost at the time. It will most likely, however, save you a bundle in the long run.