You've still got the old 12.5.4 database up and running, right?
I'd write some SQL to reverse engineer the desired 'alter table' commands from the 12.5.4 system tables. May need/want to do the 'drop index', 'create index' and 'update index stats' commands, ymmv.
I don't know the system table mappings off the top of my head but it shouldn't be too hard to peruse the source for sp_help to see how/where it obtains the partition counts, separate segments (if used), etc.