The RCCE host file lists the cores to be used by their IDs. If your rc.hosts contains the lines
rccerun will try to run your program on these cores.
Ranks in RCCE are assigned based on the sorted core IDs. So here in this example, core 1 will get rank 0, core 2 will get rank 1, and core 47 will get rank 2. If you want to preserve the order in the host file, just remove the RCCE_qsort() in RCCE_init() in file RCCE_admin.c. Then rank 0 will be assigned to core 2, rank 1 to core 1, and rank 2 to core 47.
I hope I'm not missing the point of your question. Is this what you wanted to know?