1) That happens to me sometimes too, but by no means all the time. It generally disappears after a day or so. If it’s red and itchy or oozing gunk, its more likely to be an infection, in which case you need to get some antiseptic cream on it or consider seeing a Dr depending on whether it looks like your leg is going to fall off. I’ve never had an infected site but apparently they’re not nice.
2) I don’t think it’s recommended for hygeine reasons, but in the real world you can refil the reservoirs if you want. Here’s how I do it with a Medtronic pump:
Disconnect your infusion set from you and remove the reservoir from it and the pump.
Rewind the pump (via the Prime menu)
You’ll probably need to get the connector bit (that goes between the reservoir and the insulin bottle) from a new reservoir because you’ll have thrown the other one out after your previous site change.
Fill up the reservoir as you would a new one
Reconnect the reservoir to the old infusion set tubing and put it into the pump.
Prime as normal (won’t take long as the tubing is already full of insulin)
Reconnect the infusion set to you. No need for a fixed prime as the infusion set still has the old insulin in it.
Personally, I’ve only done this a couple of times. Normally I just change the whole lot as I figure its not worth the hassel of doing the reservoir one day and then the infusion set the next.