Sometimes changing the words to other ones is improvement (using words that are better descriptive (e.g. "firefighter" instead of "fireman"; their job isn't to light you on fire, isn't it?), removing distinctions that are irrelevant or unknown (e.g. words with "-ess", which I think that you usually should not need such a suffix), etc), but sometimes not.
About renaming git branches, the change that GitHub made is harmless, and made improvements too, since you can easily change the default branch and rename branches, which is useful for other purposes too. Furthermore, the name "main" is shorter than "master", so there is that advantage, too. The first two letters are also same; I don't know whether or not that might sometimes be an advantage. However, maybe if it were named "trunk" by default then it might be more consistent with other version control systems that use the name "trunk" by default; although, even if it isn't, that isn't a problem either since you can still change the default names anyways. (Note: I do not use git or GitHub, so if I have any incorrect details, then you might add a comment with the corrections, please.)
In SQLite, they changed the name of the schema table from "sqlite_master" to "sqlite_schema" (although the old name still works too). The new name is better descriptive of what it does, but I would have consider it is not worth to change this, so now there is two names, etc. I would have waited for SQLite4 and changed it to "sqlite_schema" in SQLite4 (and remove the name "sqlite_master", then), instead, but now it is what it is, and it would be better to keep it how it is instead of changing it back which would be even worse.
About "priest"/"priestess", I should think that it should depend on the roles of religious traditions, independently from the gender. (For example, Christian traditions do not have a separate "priestess" role (although some traditions ordain women, but it is not a separate role from men and so the term "priestess" is inappropriate), so should not need to use that word. Some (non-Christian) traditions might not have priests at all.)