you can change an object's year appearence (and disappearence) in the _targets.ini
Obviously, they must be listed in the _types ini with their "ActiveYear=" statement, but you can turn off and on individual entries in the targets ini
This, for example, is from the unfinished Modern Hawaii rebuild:
Target[081].Type=IOWA
Target[081].Offset=105.00,587.00
Target[081].Heading=310
Target[081].ActiveYear=1998
TK did something similiar on the IME map, where he turned off an entire airbase (down in the southeast corner of Israel)
So, you can have a Zil from say, 1955, and replace with a GAZ (or whatever) in 1985 -these years are just examples. It would look something like this:
stupid copy/paste isn't formatting right, but you get the idea