No, not in keywords…
When you use regex (in Related words) it only works if you name it(in Keyword name) same as string in regex.
again exemple:
((?i)weather[a-zA-Z0-9]*)+[ -.+_]((?i)today[a-zA-Z0-9]*)
name(Keyword name)has to be “weather today”, if you write something like “todays weather conditions in london” it will not work.