Robot,
For the swelling... First thing you need to do is get the wood dry. Suggest leaving it in a warm dry place till it loosens up again. If it's warm where you live, I recommend the dashboard of your car in the sun.
Once dry, you can adjust the tension. Put a large screw driver in the well and twist it to expand the inner collar a small amount. Go slowly. Some amount of tension keeps the knife safer.
Once you have the tension where you want it, get some carpenters beeswax at the hardware store, break off small bit and shove into the nooks and crannies of the joint. Melt it in with a hair dryer. Do this with the ring off to keep the ring from getting fouled. Do this a few times and you should end up with a fairly good seal on the wood. Repeat as needed but this is the best approach I've found.
Sticky lock rings can have a lot of causes. If the matter is just a bit of dirt or sand, ignore it. It goes away and doesn't hurt anything. Most sticky or grabby lock ring issues will go away with use and the ring and inner ring wear in. But if you want to hurry along the process, I recommend taking off the ring and marking the inner ring with magic marker. Put the ring on, work it back and forth a bit, then take the ring off and look for scratch marks in the magic marker. This will tell you where the grinding is coming from.
On a new Opinel, the most common spot I encounter is the inner edge of the slot in the ring. I often sand these edges down with 400 wet/dry sand paper. Another common spot is the top of the rivet heads. Same thing. Polish them down a tick with 400 grit paper. Some Goo Gone will clean off the magic marker ink.