Could this new IR have an impact (positive or negative) on the way the module is evaluated? Yes, and that is the main purpose of changing the IR.
Will the fused nodes be compiled and/or scheduled differently? Or this only affect the symbolic tracing? Changing the graph will probably alter the scheduling of the node since “fused” nodes will be scheduled as a whole kernel, while the folding of such fusions will have separate schedules. Symbolic tracing is one procedure to capture the graph and thus changing the graph does not affect the symbolic tracing procedure per-se, but it does affect the result of the symbolic tracing.