So those earrings that came with Showtime for males... I don't normally use earrings on my male Sims, but if I ever do, I'd only ever use the single left one, at least with the hoops anyway, yet for some reason EA only put the double hoops in and not single ones.

I want to find the mesh file so I can get rid of the right one, but I don't know how to track down and find the correct mesh file in the enourmous fullbuild files. I'm using Postal by the way.

Also, I would be right in thinking you can edit mesh files (regardless of whether they are clothes, accessories, hair or objects) in Blender, yes?

amaccessoryep6earringshoop is the file you want.
You should be able to export the GEOM file and open it in Blender.(with the correct plugins)
Do not export it as obj file, you will lose the boneassignements then.(but as hex)

In Postal you then start new and import the just exported file, you might have to fix the group and instance numbers.
Save it as package.
After that reopen the package with Postal and import your custom mesh

Yeah, I know. But those names don't show up. Just a bunch of strings and numbers.

Only in the .bblend files, I found a name like that, and that was having to go through all the files individually to see if they contained that name (as they do not show up in the panel if you know what I mean) I couldn't find the GEOM file related to it...

With The Sims 2 in SimPE it was easier as the names showed up on the panel and you could sort it and find it easier, but I can't seem to do this with this one, hence why I'm asking an easier way to find it.

You can try with S3PE IT has a search function.

In postal i always ticked the top tab so all is in alhabetical order, shouldn't be to hard?
You are looking in the directory of Showtime right?

In Postal you have to click Workspace / Show Nmap Names for the resource names to show up. And like Bloom says you should be looking in the FullBuild0 for Showtime.