Re: Peavey 12" stage monitor used as a cabinet?
Hadn't realized modding the cab was an option. In that case, disconnecting the horn and crossover would be the best way to go. If you simply disconnect the horn, you'll lose all of the highs, and even though speakers do naturally roll off a lot of the high end, I don't think the sound would be great if you were hearing only tones below the crossover frequency. However, with the amp hooked directly to the speaker the sound might be pretty good- depending on the quality of the 12". Years ago I had a floor wedge loaded with an EVM 12" to use instead of my 4x12 when the stages were very small. It sounded quite nice actually, not too much of a sacrifice in terms of tone.
If modding the monitor is not an option, see if there's a knob for controlling the horn level- this used to be pretty common but I don't know whether it still is. Some speakers may still have it. If there is one and you can spend some time with it, you could experiment with rolling off the horn until your tone sounds more natural to your ear, then put the monitor out of the way once you've found a decent balance.