It is possible to Zero and Span (re-ranging) and adjust variable on the LD301 without having a HART communicator.  This is accomplished through 2 holes in top of the transmitters, right below the certification plate, and using the Smar Magnetic Screw Driver.
Before doing any change, it is necessary to make sure the transmitter have 2 internal jumpers set to the right position. These jumpers are verified before the installation on the field to avoid any hazard.  If the transmitter is already installed and you are in a classified area, take the transmitter to a safe are to make the jumper configuration.
Once the transmitter is in a safe area, remove the cover that protect the electronics and locate the jumpers in the top part of the electronic board.
Each jumper base counts with 3 golden posts or 3 aligned holes (this will depend of the transmitter version).
The jumper itself is a 2-pin short and can be place in the 2 pins on the right or the 2 pins in the left.
See below the possible combinations and their effect:
Here is a summarized explanation for each of the above combination:
You can find this information and more details on the LD301 Manual on section 4.