Selfreference is a very common feature when working with variables, i.e.:
myString = concat(myString,'blablabla');
myArray = skip (myArray,1);
However, current Flow "Set variable" action block implementation does not support it, so you are forced to duplicate variables and declare an auxiliar one everytime you need selfreference. The only exception I've found so far is with int variables, as there is already an "Increment variable" action block.