With the booster pump, what is your actual pressure?
Also, now with the booster pump, you probably have a check valve in the system that may not have been there before. This can cause excessive pressure caused by expansion when using hot water. The cold that gets heated expands, and if you don't have an expansion tank to handle it, the pressure can rise quite high. That high pressure from expansion could cause a toilet (and other things) to leak where they didn't before. Pick up a pressure gauge if you don't have one now in the system, and monitor the pressure after say taking a shower to see what the pressure peaks at.
You'd need to shut off water to the house to replace the shutoff for the toilet...get a 1/4-turn valve rather than a multi-turn one...they last longer (the ball valve doesn't leak as easily as one with a washer in it). You may not get a major spray if the toilet's shutoff doens't stop the flow completely, but depending on the flow, it could spray all over; best to shut the house off while dealing with it and the repair.