[Raptor]

That sucks, never tried replacing one with engine and crank etc all in, but you should be able to do it easily enough, you might have to rotate the crank out of the way but you should be able to get in there with a long extension.

As far as running it, the valve isn't in that part of the squirter so it shouldn't stay open or otherwise, in that respect it "should" be okay to run it. 3 pistons will be cooler than the others. As long as you have the pan off anyway, I would just replace it since it really shouldn't take too much time, like 15 minutes tops including cleaning the parts.