Removing rank (which is an optional plugin), removing callsign (which is just a demographic field like any other) and making position freeform are all things that are supported via configuration options. You shouldn’t need to touch the code for any of that. If something doesn’t work right, let me know.
(Though it’s expected that position will be short-ish like ‘Artist’ and not a huge thing like ‘Proprietor of the Crazy Art Studio’. Long position names will be truncated on the in-game profile, but should show up fine on the web portal.)
If you want to make more in-depth changes to the layout, I would suggest doing the basic coding tutorials first. There are four separate tutorials that walk you through all the important building blocks of Ares code. The template system (which is what controls the layout of things like profile, sheet, and more) is introduced there and covered in more detail in the Advanced Templates article.