To say that He set aside His limitlessness implies firstly that the Sefirot are not something new that was not already included in Eyn Sof, blessed be He. Prior to the Tzimtzum, the Sefirot already existed on a plane of limitlessness, and this is what He set aside in the Tzimtzum. The second implication of saying that He set aside His limitlessness is that as long as the Sefirot were totally subsumed in Eyn Sof, we cannot say they existed in the same way as they do now.
We must say that they existed in some other way. For the difference between existence within limits and existence on the plane of limitlessness is not only one of quantity but also of quality. In their unlimited aspect, those same Sefirot had a different quality: they existed in a different way. If so, when they took on limits, they received a new quality.
This is the sense in which they were an innovation. Through being revealed within limits, they came into being in the way they exist now, and this is the innovation.