The PCRE and PCRE2 regular expression libraries have the ability to change the case within a replacement. For example,\U...\E and ```\L…\E`` cause the enclosed substituted expression to be done in upper or lower case, respectively.
It appears that the oniguruma library used in 010 Editor doesn’t have such a feature, in which case implementing this in 010 Editor might require a change to some other regex library and a lot of rework and testing for you.
There’s a fork of oniguruma called onigmo but I haven’t yet discovered it if offers case conversion or not.
Case conversion aside, Onigmo might be worth considering as a replacement in 010 Editor for oniguruma, unless 010 Editor has a dependency that is already dragging in oniguruma, which might make it harder to switch.