Does anyone know if it's possible to change the transfer box oil whilst vehicle is on the floor , but in off road height ?

Many thanks

Yes it is straight forward enough with a simple drain and fill / level plug.
Both are an 8mm hex and have a copper sealing washer.
These can be reused but it's safer to get new washers. 2012 TDV8 4.4 Westminster Santorini black
2016 Discovery 4 Landmark
2002 Defender TD5

Yup … put it in off road mode for more access … although it is advisable to still have something under it to catch it just in case it wants to drop down whilst your under it. Doesn’t need to be taking weight off, just placed to take weight if starts to drop. V8 or else ...