It's convenient to use Edit -- Replace tool to change part of a formula
string with repeated characters, but strings that starting leading by the
asterisk mark (*) seem to be an exception, for instance, if your want to
replace a selected area with something like b7*sum(....) to b7/sum(...), you
input find "*sum(...)" replace by "/sum(...)", all you can get is "/sum(...)"

Maybe (*) is reserved by Excel, but are there ways to solve this problem?