I am not an expert in warehouse racking, but this sounds like a serious breach of the W@H Regs to me (more info needed to be certain) Stick to your guns.

You are not alone, this is common place... Be rest assurred that you are an interferring 'elf n safety because in this instance that is what is required of you in order to execute your duties. First issue, you control the contractor... the tail does not wag the dog! Second, you pay him for a service you want not a servise he wants to deliver.

There is a problem here, if you were having a new installation then the build would enable installers to fit by the method you describe however, when adding to an installation then access to complete the task may not be straight forward in the covential way i.e accessing to fit the rear beams.

It is common for racking installers to have a requirement to leave the platform in order to perform their duties, and as long as this is controlled then there should not be an issue... they should be wearing servicable harnesses and attached to a suitable and sufficient anchor point prior to leaving the platform.

As I see it, the only other way to achieve this would be to remove the front beams on the bay in order for a lift to access the bay and fit further rear beams... this is generally unpracticable as removal of the front beams weakens the whole structure, so this could only be conducted safely on an empty structure... the strength of any racking configuration is in the configuration 'mass' not the individual components... think Jenga!

Racking installers hate wearing harnesses and hard hats (persons operating at ground level need hard hats when others are working above), they will tell you anything to get out of wearing them so you must not only be clear on your requirements - on your sites, but you must also monitor them (not 100% but periodically).

One point you failed to mention although you may have it covered... if they are adding to a configuration then this must be as a result of a re-design for the 'whole' configuration, not just the bit they are adding (think Jenga again) i.e. it needs re-designing by a competent person, not simply a racking installation operative. New Racking SWL signs should be provided by the contractor. I would suggest this needs to be to SEMA guidelines by a SEIRS registered company.

Hope this is of assistance.

Agree completely with PJG.

One point worth mentioning. You can use MEWP's to access high level locations and people can leave the basket, BUT you need two safety lines and appropriate anchor points. One line remains anchored to the basket until you anchor the second line and then remove the first, and the reverse coming down. The anchor points might be problematic if they are modifying the racks - how can you be sure it has enough load bearing capacity?

Sorry to be a pain but please don't forget you need a rescue plan for this sort of work, how do you get someone down if an incident occurs in time to prevent suspension trauma? It might be difficult between racking where space is limited!