You can remove and replace the pump with the tank reading about 1/2 full as you said. the only concerns are that there may be fuel vapours that could explode if exposed to a spark. Ive done the job a few times (once in my X on the side of the highway)
my procedure was simple.
- unlock the doors on the X5 and open the rear hatch.
-disconnect the battery (no short cuts here, just disconnect the negative terminal.)
- lift out the lower rear seat, with the rear passenger door open (the access point) carefully peel back the sound deadener, and disconnect the electrical connector, then fuel hoses. make sure you have a fair collection of rags and paper towel around!, carefully pull up the pump, take your time to let the fuel drain into the tank. be careful not to let any dirt or debris fall into the tank!! once you get the pump out, you have to roll it to one side or other to allow the fuel level sender to exit the hole. once you have it all out, place the new pump in connect the hoses and then the electrics but before you put the seat back in, connect the battery and test it, you should be able to hear a whirring sound for about 2-3 seconds as the pump primes the lines.
then start the engine, it should come to life and show the fuel level in the tank.
good luck!

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.