The next issue is who makes tires and tubes in 540 mm, are they good for your purpose, and will they be at the LBS that you limp to on the next ride. In my experience, at least, there are only a few choices and they are only available mail/online.
The one bike I restored that had 540 mm rims (actually French 600A which is 541 mm), I replaced with narrow 559 mm (26"/MTB) rims for which there is a good selection of tires and tubes, and a decent chance of finding one at a LBS. Also easier to find said rims used, and in the correct drilling (# spokes) for your hubs.
Check your brake caliper reach and frame clearance, to see if this is an easy swap.