Most of the Welding supply stores will just swap out the bottle. But if your bottle is old and out of date no you will need to buy a new one and go from there.
In the weldinig industry most all tanks that are 4 foot and smaller are considered owner tanks. I buy a bottle the first time then just pay for the gas after that. When I run out they just bring me a filled one and swap it out. This way the stores can keep the newer bottles in the supply chain and weed out the ones that are going out of date. As for gas they have almost any kind you can think of in a small bottle like the CO2 I have oxygen and ac. plus also a small bottle of nitrogin that I use.