This post tells you how it can be done, but it's not easy:
Fundamentally, the reason this can't be done with variable names is that KM is so powerful that variables names can be constructed on the fly, or they can be buried deep within script actions. There is no way to "locate" a variable unless you actually RUN the macro, in some cases. Compare that with macro names - if you change a macro name it is immediately changed in all the Execute Macro actions across all macros, even if the macros are disabled. (Although if you put a macro name into a script, it won't catch that copy.) This prevents all kinds of programming errors, but means we have to go to a lot of extra work to execute a macro whose name is stored in a variable.
The Architect said 3 years ago that there was no plan for a general Find and Replace at this time.
However I'll tell you what I'll do. I have a sneaky way of creating a macro that runs in the background and can generate a beep whenever it "sees" a name of your choice on the screen. That will almost be half as good as a "Find" ability in the KM Editor. I'll go write it now, and place it into the Macros forum.