[grreefkeeper]

Scoring glass works just fine (cut all the baffles for mine this way) but you need to go ALL the way from one side to the other. With it already installed you will not be able to do this as you will leave just a little unscored on either side. How much room do you have for your skimmer? I would just make a stand for it to raise it up, has the same effect as a lower water level.

 

[grreefkeeper]

The good glass cutters have oil in the handles for better cutting then it takes special pliers to get a good clean break, I say this because my wife does stained glass and she has tried a lot of the cutters and pliers, I think you are going to have to take it off line and replace the baffle at least IMO

You don't want to use the oil cutters as they may contaminate your tank. As for the pliers they have a wide sharp edge to "grab" the score to break it and are very useful. I still feel that you will most likely end up with jagged edges if you try to do it in sump (it should be taken "offline" as Archer said). I would recommend trying a different method. For the time it takes your tank will be fine (much better than a power outage). Cut the baffle, rinse the sump, reinstall. Oh yeah, make sure to scrape the silicone as already mentioned.

My .02