As mentioned if the ballast will support driving additional bulbs yes. You will have to get to the ballast and look for the details. It is hit an miss from my experience with t some fixtures that did slap in ballasts that would run additional bulbs. Depending on what you are looking to do easy to find used ballasts as many of us end up saving older stuff for future builds. With the leaps in lighting I would imagine many have ballasts laying around that will likely never be used.