LDN - Luminis Developer Network

Luminis version I worked on is "4.1.0.0 build 565".

Does any body know how can we avoid email sending to the user when adding or deleting users from a group.

I try to comment the prmpt in
$CP_DOC_ROOT/ipx/grouptools/lib/JSUtil.jsf

so when I add or delete member from a group, no pop out window which let me to enter the email contents, but email still sent out. If I worked on development env, how can I do not let the function of email work?
Thanks!