Which existing string? The Expression string (param 1)?
It won't change the case of the expression string.
Though it will only work if the entire searched for string is all one case.

>I can't do the 'first' because it will change the case of the existing string. >
>
>>You mean to replace, e.g., "VALUE" or "value"

>>The first is easy

>>lcReplace="Test"
>>lcExpression="This is a test TEST"
>>? Strtran(Strtran(lcExpression, Lower(lcReplace), lcReplace), Upper(lcReplace), lcReplace)