For a particular load resistor, say 75ohms 10W, it is always fixed. If you dissipate more than 10W, the resistor will burn. Only you can do is to reduce the power rating by sharing the power.
If you are connecting the same load in parallel, the current drawn will double-hence the power delivered by the source will double. If you connecting same load in series, the current drawn will get half since the resistance is doubled. so the power delivered by the source will get half.