Problem with swapping E0 for E1 (TEVO TARANTULA MARLIN 1.1.x)
At first it was unclear from where the snippet you posted is taken from as it was not stated in the question (this has now been addressed by a moderator edit).

Depending on the value of EXTRUDER_USE_E1 (and where and how it is set) the underlying code of the if statement will be carried out. Albeit said, swapping lines will not work, if you want to use the E1 connector of your motherboard, you have to make the printer think that it is using the E0 while it is redirecting to E1! This implies that you need to assign the pins of the E1 to the E0 extruder (so swap the pins, not the lines). This has been explained before in this topic by editing the correct pin layout file of the Marlin firmware.



EDIT : Further investigation shows that you have a custom Marlin for the TEVO Tarantula and are using the fork of Marlin maintained by JimBrown (this is essential information for your question). I have looked into the files, the only thing you would need to do is define the constant EXTRUDER_USE_E1 in your configuration.h file:

//#define EXTRUDER_USE_E1


to:

#define EXTRUDER_USE_E1


So do not swap anything. Once this constant is defined, the pin re-allocation is done for you automatically! (see the pins_RAMPS.h file)

Basically, this is exactly the same as is explained in topic How to change E0 to E1 on Marlin 1.1? and hence a duplicate. ;)