Each replace_metadata line is checked in order for regexp and conditional match. So the first one will be applied.
However, if the changed value matches a later line, that later line will also be applied.
A completely made up example:
Code:
replace_metadata:
genre=>Sci-Fi=>SF
SF=>San Fransisco
Sci-Fi would be converted first to SF, then SF to San Fransisco. Reversing the order of the two lines would prevent that in this case.