Nim's roots are firmly in Pascal and Ada, which are both case insensitive; Every editor supports case insensitive search so I don't understand what your problem is with case insensitive identifiers.
"Basic refactoring tools" would just need to replace the case sensitive search with insensitive. Every editor knows how to do that.
If you're talking about the underscore and first letter rules - yes, they're different, and that's why nim includes nimgrep, and support was added for just about every editor under the sun already (Emacs, VSCode, Vim, Sublime, TextMate at the very least). It's still Ctrl+F
I find it a big nuisance to use different casings in my code, but obviously people are different. Most of the type you won't be using the style insensitivity though, so for the most part a simple case-sensitive search will give you exactly what you are expecting. For more complicated things though you have nimgrep, and also nimsuggest (and soon nimlsp) which gives you editor support for finding and renaming identifiers. It really is a much smaller issue than people think it is.
This is such an incredibly small inconvenience, I have no idea why the Nim language would choose to make identifiers case/_ insensitive. Basic refactoring tools become unnecessarily more complicated.
Just searching for an identifier is a complex regex instead of what should just be ctrl+f.