This has been asked before but I can't find it, so will draining the gearbox (5sp newage) with the front wheels up on ramps impair draining..?

Also, same for rear diff, only rear up..?

Refilling can obviously be done on flat by rolling car off ramps..

 

The rear diff will be hard to drain fully with the rear of the car up on ramps. But you could suck the remaining oil out, if you have something suitable
The gearbox too won't fully drain as the plug is towards the front of the casing.
I did mine with a trolley jack (+ axle stand), lowering the car to let it drain.

 

Humm, I thought as much, may have to get it done on a lift..