In each of these solutions, in the round order given, there is a way of replacing one letter with “EFF” to make a new word. (This is the “way that EFF could jump in to help with each answer you’ve found”.)
INKABLE → INEFFABLE
INVECTIVE → INEFFECTIVE
JO → JEFF
LACE → EFFACE
TORT → EFFORT
SECTOR → EFFECTOR
The replaced letters spell the answer KVOLTS.