If there is zero rake in both sets (i.e. that steering stem is paralell with fork tubes) then more offset reduces trail, and less offset increases trail. Exactly how much depends on the actual rake angle, but would be around 80 percent of offset change. So basically, 1/2" of change in offset will change trail by around 3/8" (or 10 mm change will give around 8 mm change in trail)
I do believe the Ceriani triples are fairly close to the Yamaha triples, but checking won't hurt.
Just an example: When people use 90s USD forks from a Ducati on a 70s Japanese bike, they end up with a lot more trail than the bike had originally.