I have a Yamaha FG423S with chrome tuners and I've just bought an Epiphone Hummingbird Artist with ivory colored plastic tuners. I would prefer the chrome on the Epi, is it possible to just swap them? Are tuners on acoustics all made to a standard size?

I've never done anything like this before, do you just unscrew the bottom and they pop right out and back in simple as that? Any tips for a noob would be appreciated!
No, tuners are not standard sizes, afaik. to remove them though, it's usually just a matter of removing the screws.
hhmm, that figures! So how can I tell if the chrome ones fit the Epi? Just give it a shot? If it fits it will fit snug in the hole?
if they do fit, they will just fit in. if they're hanging loose/you have to force it, they obviously don't fit. Common sense really, but apart from size differences, there's really no other factor to consider for acoustic tuners as they're generally all 3+3(three on each side of the headstock).