pattroughton replied to your post “I was thinking about Bajorans and their earrings and how they are a...”
They did say that Ro being able to keep her earring was with special permission, which would imply that your average Bajoran in Starfleet was not permitted to wear them. Tuvok enforcing it with the Maquis would seem to confirm that.
You refer to the episode “Ensign Ro” from TNG when Riker had Ro remove her earring when she first arrived on board according to Starfleet Uniform Code. Later she made it a ‘condition’ that she be able to wear it if she fully returns to Starfleet as Picard offers her a position. Considering that Worf’s sash would also be a family designation similar to the Bajoran earrings, it’s safe to assume that the particular code (as it’s not quoted) is one that is adjustable much like modern military uniform codes.
For example, hair buns in the military can be shifted depending on your superior at the time is. I had one who wanted uniformity and specifically in that way what was referred to as the ‘sock bun’ (or donut bun was another name). While this was not a set ‘dress code’ it was regulation we had to follow as our superior required we follow the code in that manner. You could, of course, just cut your hair short and then not have to put your hair up. When Ensign Ro beamed about the Enterprise after having been gotten out of prison and had a poor history in Starfleet. Riker greeted her in the strictest SF manner possible, a ‘no non-sense’ attitude.
When Kira puts on the SF uniform in DS9 she keeps on her earring. Sito Jaxa in a later TNG episode does not. A Bajoran engineer in Insurrection is seen with on. However, Bajorans are seen not wearing their earrings, just like not all Klingons wear sashes or their family badges or armor. But for SF to go “oh yeah Worf you can wear this sash that is completely against regs but you Bajorans can’t wearing the earrings that have been a part of your culture for centuries” would be completely against what SF is about. So, it likely comes down to, as it often is in the military, command based.
Training is going to be more strict. Uniformity across the board. No earrings, no make-up, no special anything to designate you different than anyone else. Hair cuts the same (unless female then you just have to all have your hair up if long). If going through officer training you get cadet ranking system if going through enlist congrats your are now just some recruit or whatever they decide to call you. Once in the fleet it’s your commands/units choice and then yours. If it’s a “yes you can wear it while in uniform” it’s then on your to pick. If they say no, then you just don’t in uniform and put it back on once out of uniform and be sure to remember to snatch it off once you put on your uniform.
Starfleet would have a list of acceptable cultural items that would be permitted in uniform due to this or that reason. I don’t recall when but Spock wore the IDIC symbol during TOS. To restrict one entire species from wearing what is a culturally accepted practice amongst them for centuries while not restricting others (Vulcans, Klingons, humans, etc.) would be rather against what Starfleet is about. Sorry for the long response, it’s just that Ro’s particular case wasn’t an ‘exception’ it was a condition of her return given that she was given more strict boundaries due to her particular behavior pattern.