>>214503883
Yeah the white box thing is proper stuck onto the wall and cannot be moved once its plumbed in.
Off the back of that, it's worth considering before they arrive where the router's home will be once it's all set up and asking them to put the white box there. This is because your router and the white box will be connected by an ethernet cable. They will try to suggest you put the white box as near to the hole on the outside of your house but this is only because it means less work for them running the separate fibre cable along skirting boards / around doors etc.
If there's a specific room / place that you know you will be having the router (for maximum wi-fi coverage etc) then be firm with them that that's where you're putting it. You are allowed to specify where you want the white box. If you forcefully tell them you want it in X room and nowhere else, they are obliged to run a neat fibre cable from the exterior hole throughout your house to your desired spot.
Again, they'll try to pressure you to put it close to the exterior hole so they can get away with spending less time stapling a thin fibre cable to your skirting boards. But don't be pushed around, you tell them where you want that white box lad.