How do You concatenate a value to an array that was retrieved through a query in sql?
However, if, for example, I attempt to add the string 'there', to the array of strings '{fellas,ladies}' which correspond to the word 'hi', nothing appears to happen:


You are comparing the value of the column word with the string constant 'hithere' - you are concatenating two string constants, not a string to an array column. 

 where word = 'hi' || 'there';


is the same as

 where word = 'hithere';




It sounds as if you really want: 

SELECT mkvword || 'there' 
FROM mkvtable 
WHERE word = 'hi';


If you want to change the value that is stored in the table rather than just displaying it, you need an update:

update mkvtable
  set mkvword = mkvword || 'there' 
where word = 'hi';