For the BR-MLX-100GX2-CFP2 module there should be no restrictions, this type of module only occupies one slot, so you can insert it in any available slot in the chassis.
The older documentation that you were referring to was probably referencing the BR-MLX-100GX-2 module. This module was released earlier and occupies two interface module slots in the chassis, requiring the chassis slot divider to be removed to install it. This type of module has one slot active and one slot inactive. In all devices, the lower number of the two occupied slots becomes the active slot.
The BR-MLX-100GX2-CFP2 module replaced the BR-MLX-100GX-2 module and only occupies one slot, so it does not have this restriction.
I hope this has answered your question.
