The ability to refill/swap the tanks will come down to how the gas suppliers in your area handle the practice. Around here, they look first for the neck of the bottle to have a gas vendor's name on it. Either stamped into the neck ring or *forged* into it. *Stickers* do not count. Paint markers do not count. If it has a name such as AirGas stamped or forged there, then you will be forced to deal with that company. Then that vendor MAY treat it as THEIR property, unless it's of some off-size that they reserve for (and sell for) personal ownership. Only the branded company can tell you what you are looking at.
However, there are also bottles that do not have a stamped neck, that are smooth and unmarked. These are called "slick necked" bottles and are treated as personally owned, not rental bottles. You will prefer that your bottles are slick necks. MOST gas vendors (again, speaking to my own area, you'll need to research yours) will simply swap you a full slick neck for yours and charge you only for the product, not the bottle, and it will not be a rental.
IF (it's a big *if* because they often don't) they check the date on your slick neck and say its too old to swap, just say thanks and take your bottle. Then take it to another gas vendor see if they'll swap. They probably will. Their bottle plant will re-certify the traded in bottle and re-date it before they fill it. No reason for that to be your problem, IMHO.
Because the slick neck is used as an indicator of private ownership, it has real value. Do NOT--- I repeat DO NOT--- let them swap you a branded bottle for your slick neck!
Edit: If it is stamped with the name of a now-defunct gas vendor, you should call around to see if any current vendor is now servicing that company's contracts. If no one is, they *might* treat them as slick necks or they may not take them at all(?) If stamped like this, THEN paint markers and stickers will provide a link to who services them.
