Assuming the pump is on land, Just cut in a reducing T close to the pump discharge and either connect a 5-10 mm line/hose going back to pond or same with a spring upstream pressure regulating valve set for slightly less than the pump deadhead pressure.
pump will turn itself off every night , correct ?
is the pump for the line from the lake to the tank also submersible? If so, dead heading should not matter.
it would help if we knew where there are check valves and other valves in the lines between the lake and the tank. Also, brand and model of pump, self priming, etc.
most atmospheric tanks will have a vapor vent line on the roof to handle overflow conditions. If not, then rupturing the tank at a bottom seam is possible since the piping is usually stronger.