There are some playing techniques taking different meaning depending on the composer or the context. Take, for example, the tenuto sign (-). Sometimes, it means that the note is just a bit shorter than full duration. Some other that it is to be stressed, and last until the next note. Some other, a milder sforzato.
Expression maps can just assign one of these meanings. One can easily modify it for the specific piece, maybe changing the name to avoid overwriting the ‘master’ expression map.
However, maybe there is a way to assign multiple meaning to a playing technique in the end-conf/expression map combo, and choose the correct one for the context in the playback options and in the event properties.