Increase caster doesn’t really change wheelbase since you are tilting the kingpin on it’s center axis. Gerard is referring to when you run neutral caster (both pills facing the same direction), it actually moves the whole spindle forward or backward without tilting it.
I haven’t actually tested changing the wheelbase like this, but it is only changing the wheelbase a couple mm so I wouldn’t think it would make a huge difference. But I know on the old ART kart which had adjustable wheelbase on the rear cassettes, just 10mm made a pretty big difference in how the kart handled. Maybe @GerardVanGaalen has some opinion on it as well.