I haven't played with it much myself but you might take a look at this
post in the FFDL plugin thread. Particularly look at the replace_metadata settings shown under the spoiler cut. These are settings that you add to your personal.ini under FFDL's Configure Plugin option.
You'd probably want something along the lines of this:
Code:
replace_metadata:
fandoms=>Harry Potter \-\ fandom=>Harry Potter
fandoms=>Harry Potter \-\ J. K. Rowling=>Harry Potter
fandoms=>Once Upon A Time \(TV\)=>Once Upon A Time
fandoms is the custom column, the middle section is the incoming metadata being downloaded, and then the final section is what you want FFDL to convert that fandom to. In other words (Harry Potter - fandom) becomes (Harry Potter).