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Easy!
You have two options - one, is to create an intelligent playlist with the criteria you want, so you could have an "All House Except Electro" playlist that constantly updates with all the tracks from the House genre tag AND the various MyTag options you select. This works well, but only if you keep using those same sub-genres in the inclusive list.
If you want it to be a bit more dynamic, try this:

1) Open the filter view
2) Check the Genre box
3) Select the genre you want to use (in your case; House)
4) Check the Custom box, make sure AND is blue
5) Click the sub-genre tags you want to include