Rob,
There are lots of posts about pen sets and standards with critical information here. But, you and others have my sympathy for not being able to find them as the forum "Search" link above will not search for anything with 3 characters or less ("pen") among other deficiencies.
Use Vistasp's custom Google search page to search for topics concerning pen sets:
http://archicadstuff.blogspot.com/
In the posts that you'll find will be some by Link and me noting that certain pens are used as the defaults by library parts in the standard library. Minimally, pens 1 through 10, 19 and 91. Plus the gray scale. Link noticed another dozen pens by thoroughly examining the entire library.
Changing the thickness of these pens in your pen sets will change the default appearance of those lib parts. In general, it might be best to leave them alone and to use any other pens as your custom color/widths.
In the case of the light symbols and cabinets, as Stuart notes, your only real option is to use a different pen for one or the other - e.g., change the parameter for the placed object(s).
(You can play games with overlaying a cabinet view - with one version of pen 4 - on top of an electrical plan view - with a different thickness for pen 4. But that gets unwieldy pretty quickly.)
In the (hundreds of) posts about pen sets, you'll find some people who assign pens-per-function, and others who use a small number of pens-by-width. Depends on the amount of complexity you want to manage, as well as how many different ways the same item needs to appear in different drawings.
Cheers,
Karl
One of the forum moderators
AC 27 USA and earlier • macOS Ventura 13.6.9, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB