I've got a bunch of lamps from Europe that I want to use where we've just moved in North America. I cut off and replaced the plug on one lamp with a North American one and it works fine. I'll be doing the others. But I have an air purifier that works completely fine at 110/220V and 50/60Hz. It only uses a two prong plug. Is that likely just as easily replaceable/modifiable as lamp cables or are there gauges of wire to consider, amounts of power, different ratings of two-prong plugs, etc etc?
First, I really don't advocate splicing new plugs onto old wires unless you really know what you're doing. Many of these devices likely have UL listings, which help ensure their safety in a residential context, but which also depend on the system as a whole, unmodified.
If the device says 110-240VAC and 50/60Hz, then you can simply use a plug converter, no need to splice.