Whew, being mighty bold but you ~might~ be able to get it to work...
I'd do everything with the library NOT available to the system, this MIGHT
allow you to clean out references to volumes not used on each system without
causing them to roll scratch.
Even if you do this you will still need to go in and alter the category of
the tapes bind private volumes to the new private category of which ever
server you set new categories for (be it the new one or the old one)
That is, say your existing server is using 300 & 301 for private and scratch
categories... your new/other server, you will need to alter the private &
scratch categories to somethings new like 400 & 401
for that you can use something like
        mtlib -l/dev/lmcp# -C -VABC123 -s012C -t0190
AND remember, just because you have collocation on doesn't mean the data is
fully isolated ! ! !
You still might have data from one node out on a tape with data from another
node.

About the only way you could test this would be to restore the DB to a test
server, delete all the data from one of your sets of nodes, then note all
remaining private volumes (make sure this box doesn't have access to the
library, and to be safe, I'd take it off the network while testing things).
Then restore the data base again and delete all the data from the other set
of nodes, then note all remaining private volumes.
If those two sets were totally unique, then your process (I believe) would
work.
If you had ANY overlap in your sets of private volumes, you couldn't perform
your task...
        you would have to do a move data against that volume to try to split
out the data on it and start over with your check.
Logically, your process ~should~ work IF all data is really collocated but
you will have to be very careful...

Dwight