I wouldn't think twice about swapping the sending unit, you have covered all the bases with safety, if you want to go one step further you can fill the tank as full as possible with fuel, the less room for vapor the more safe it will be. Many folks here have done welding on gas tanks including myself, cleaned the tank as best I could with engine degreaser, then HOT water, then fill the tank with water with the repair site as high as possible, wave the torch over the hole and you get a little gyser, then your ready to weld.
