Understand this rewrite rules so I can change it safelly?

Understand this rewrite rules so I can change it safelly?

# -FrontPage-
#<Limit GET POST>
# order deny,allow
# deny from all
# allow from all
#</Limit>
<Limit PUT DELETE>
order deny,allow
deny from all
</Limit>
AuthUserFile /home1/tenleiye/public_html/_vti_pvt/service.pwd
AuthGroupFile /home1/tenleiye/public_html/_vti_pvt/service.grp
# Use PHP5 as default
AddHandler application/x-httpd-php5 .php
AuthName tenleiyen.com
#IndexIgnore .htaccess */.??* *~ *# */HEADER* */README* */_vti*
<IfModule mod_rewrite.c>
RewriteEngine On
# Force www
RewriteCond %{HTTP_HOST} ^tenleiyen\.com
RewriteRule ^(.*)$ http://www.tenleiyen.com/$1 [R=permanent,L]
# Do not change or site will be f*ked. Restrict all except the list
below, redirecting all traffic to the index.php
RewriteCond $1
!^(index\.php|1\.ico|favicon\.png|apple-touch-icon(.*)|crossdomain\.xml|robots\.txt|css|js|images|uploads|videos|download|sitemap\.xml)
RewriteRule ^(.*)$ /index.php/$1 [L]
</IfModule>
I have a lovely note by previous programmer expressing i cannot change the
permissions. If I add something or even remove a snippet from the
RewriteCond it will 404.
I cannot:
use the root directory,
get a sitemap.xml to be read,
drop a 1.jpg file in the root directory and see it,
drop my webmaster tools .html file into the root directory to be read.
Everything is going to the index.php file and all I can do is use the
folders specified.