The lines and plus signs hint that the clues lead to words that can be decomposed into a shorter word plus an additional letter. After some inspection it becomes apparent that all of them contain a word from Extended Password, which is further confirmed by the mention of “extend” in the flavour text (though the reference to Mock Army is a red herring).
|People living in a nunnery?||SISTERS||RESIST||S|
|His swordplay was superb, with many thrusts and ________.||PARRIES||SIERRA||P|
|To where/to what place? (archaic)||WHITHER||WITHER||H|
|A Hanukkah spinning top||DREIDEL||RIDDLE||E|
|French commune featuring the Chapel of Moussy||CORNIER||CORNER||I|
This spells out the word SPHERIC. Below the clues, another set of lines with a plus sign indicates that this word should again be decomposed by removing one letter. The only such answer that is a word in Extended Passwords is