:: returning after reading first post more slowly ::
There are patterns that I might be able to do lets say 25,000 lines at a time but it involves seeing the pattern, matching and then converting to lower case. is that possible. I'll show you 2 lines maybe you can see the pattern and help.
Unfortunately you didn't show two lines. You only ended up showing one line, and you can't deduce a pattern from that.
:: vague mental association with some process in mathematics or possibly historical linguistics where you do in fact make a rule based on only one instance ::
mod_rewrite alone can't change the case of an URL. It can detect requests in a case-insensitive way, like picking up .jpg, .Jpg and .JPG in a single rule. But there's no straightforward* way to make them all output .jpg other than by individual redirects. The same applies to any mass replacement like lowline-to-hyphen (or, ahem, vice versa**).
* There's a post by jdmorgan illustrating the non-straightforward way. It relies on flags like [C] and [N] that normal people approach with EXTREME CAUTION.
** Yes, I know, it's just me. But I always think hyphens look spammy. get-your-cheap-widgets-here dot biz, kind of thing.