How can I map properties conditionally with MapStruct 1.2?

You can't really do that with MapStruct. The @ValueMapping annotation is for mapping of Enum(s).

In order to achieve what you are looking for you would need to do that in @BeforeMapping or @AfterMapping.

For example you can do something like:

@Mapper
public interface JiraKpmMapper {

    @BeforeMapping
    default void beforeMapping(@MappingTarget MyTarget target, MySource source) {
        if (source.getPropY().equals("ABC") {
            target.setPropX("V01.123.456.AB");
        }
    }

    @Mapping(target = "propX", ignore = true) // This is now mapped in beforeMapping
    MyTarget source2Target(final MySource mySource);
}

Your custom mapper then should have an @AfterMapping. Where you would convert the propX into your class. You can even do this as part of the @BeforeMapping I wrote and directly create your class (or invoke the method that does the conversion from String into a class)

you can do something like this

@Mapping(target = "myTarget.propX",expression="java(mySource.getPropA().equals(\"Abc\")?"\"V01.123.456.AB\":\"\")")