SS6.4 has new buildings
a new RC/RR will bring in new units
yes some of the SS6.3 RozMod can be used but you'll then still have to go through and change all the unit allocations for buildings, work out how to rebalance everything etc.
probably easier and less confusing to start from scratch.
your welcome to tinker with the files, but I'm on an extended break from modding for now, so won't be updating this for RC/RR.
(you may find the new CHIP megamod of interest as that will include some aspects of RozMod - but again the alltowns part will probably need to wait until after
the main mod has been released.)
Sadly there are fewer people playing SS these days - I was effectively being expected to produce customised software for individuals - not cost/time/effort efficient.