So, as I read these comments, many have some code references correct, others need to read or reread their current codes.
As a short answer, a new installation is subject to the current code, period! No where does it state you have to like it, but you should be following it. I mean this, do you intend to mean the worker safety is not important because the previous RTU was installed without that code provision? Sure hope not.
Next, some of you need to quit referencing the IRC. California does not recognize that, or the IPC or IMC for these installations, as the state adopted code. If you are in Ca., you should already know to use the Ca. adopted versions.
Next, the CMC notes 6' from the roofs edge for clearance, accessibility, otherwise guards must be installed @ 42" in height. Please note, nobody mentioned CMC 304.2, which is probably most prevalent in Residential locations, roofs 4/12 or more must have a level platform at least 30" by 30" on the service side, but if it is more than 6' from the roofs edge, that's all. (NOTE: The CBC calls out 10' from the roof's edge)
(NOTE: Guards for protection and code compliance are found where? Yes, quite possibly the Building Code, specifically CBC 1015.2 which also calls for structural elements in 1607.8. Then look at 1015.6, Mechanical equip shows you must have guards, but then it adds an exception for "Personal fall anchorage connectors") That seems like the most efficient and economical solution. It helps the fall protection while keeping the aesthetics of the roof or neighborhood in mind.
I could see where most jurisdictions would accept the anchorage exception, since it is in the Building Code. Hope this assists your current and future work!!