Hello Sebator, you may get oil from the gearbox, depending on which area it is threaded, if it is in the upper part of the box, it will not come out oil, however if it is threaded by the side (I think it goes like this) it is possible that I can throw some oil when it is removed because it is in direct contact with the interior of it.
Precautions, not many, sympleously lift the car on the right side to vary the horizontal oil level, prepare some rags not to stain the ground, and have everything at hand to be the minimum possible time with the hole discovered, and most importantly of all, cleaning that does not between shit or land inside the box.
Once the operation is done, you lower the car and check the level of the gearbox with the car horizontally, I do not think you have to fill it but just in case it is good to make sure.
All the best!