(Hope this is the right forum for this?)

You can rename fleets and you can create a custom ship design and give it its own name, but why can't we edit existing designs' names?

Your starting  exploration ship for example, will always carry the same name with a number at the end of it, with no way (that I know of) to alter it. The only possible way to get it chanegd to a different name is to sell it off, and create a new one of a custom design. This is of course not efficient and I don't think it's too hard to implement this idea.

(I found a similar thread like this but it's 2 years old so decided to start a new thread.)

Because ship upgrades are tied to design they were created from, and design is tied to its name. It's simple as that. As soon as you rename the design, you'll lose the ability to upgrade ships created from it, or even gain ability to upgrade to completely different design after several renamings, which will lead to numerous bugs and exploits.