Current setup is as follows:
2 new (hidden) columns. 1st has
=xREPLACE("((\A| |-|^|ק|ר|ש|ת))טז",[@[כרך (א)]],"$1יו")
2nd references 1st with=xREPLACE("((\A| |-|^|ק|ר|ש|ת))טז",[@HebNum1],"$1יו")
It feels like he's not using excel's built-in REPLACE function, rather 're-wrote' his own in a macro or script or something, so the nesting that excel built into REPLACE doesn't necessarily apply here. though i'm not actually sure