I have no idea if Muse will overwrite it, so please make a backup of it, or bookmark this page so you can get back what you may lose. I unfortunately have zero experience with Muse so I can’t tell you what it may do.
It might be a good idea to tell the Muse authors that their script needs amending to work on hosting where SMTP authentication is required. That way they might actually apply the necessary changes in the next version so that you don’t have to reapply them yourself.
I have been searching for a way to do this for half a month now but your answer is the only one that helped removed the “PHP not configured properly” error. However, my website still can’t send emails. I tried commenting out tls, everything. You can reproduce the problem by entering any email address at http://subscribershop.com