In one embodiment, resource availability reallocation is used in establishing one or more new designated multicast flow paths with guaranteed availability of resources currently allocated and/or used by one or more designated existing multicast flow path to allocate/use for the new designated flow path(s). These resources typically include allocated guaranteed bandwidth of a network path between two adjacent or non-adjacent nodes of the network, and possibly forwarding/processing/memory resources of a network node. One embodiment communicates multicast control messages between nodes identifying to establish a new multicast flow path with resource availability reallocation from a designated multicast flow path. In one embodiment, a Protocol Independent Multicast-Sparse Mode (PIM-SM) Join/Prune Message identifies Pruning of one or more multicast flow paths and Joining of one or more different multicast flow paths and designating resource availability reallocation from these Pruned multicast flow path(s) to these Joined multicast flow path(s).