Enabling gzip by default questions

Hello i'm thinking about optimize by default with config file of apache.

something like Enable gzip compression | GTmetrix

(and other like headers etc.) put in apache config file so clients don't need to put it in theirs .htaccess file

so my question is: is this possible?
what if i put that code, and someone don't want to have it. Can he disable this via .htaccess and how (with gzip example)?

and one more if i put example gzip compression and someone also put the same thing in his .htaccess what would happen?

 

I know that, but I am worried about other things that I have already mentioned.

Like this if i put in conf file of apache

Code:

<IfModule mod_expires.c>
  FileETag MTime Size
  AddOutputFilterByType DEFLATE text/plain text/html text/xml text/css application/xml application/xhtml+xml application/rss+xml application/javascript application/x-javascript
  ExpiresActive On
  ExpiresByType text/html "access 600 seconds"
  ExpiresByType application/xhtml+xml "access 600 seconds"
  ExpiresByType text/css "access 1 month"
  ExpiresByType text/javascript "access 1 month"
  ExpiresByType text/x-javascript "access 1 month"
  ExpiresByType application/javascript "access 1 month"
  ExpiresByType application/x-javascript "access 1 month"
  ExpiresByType application/x-shockwave-flash "access 1 month"
  ExpiresByType application/pdf "access 1 month"
  ExpiresByType image/x-icon "access 1 year"
  ExpiresByType image/jpg "access 1 year" 
  ExpiresByType image/jpeg "access 1 year"
  ExpiresByType image/png "access 1 year"
  ExpiresByType image/gif "access 1 year"
  ExpiresDefault "access 1 month"
</IfModule>

what if someone want to turn this off or want to change "access 1 month" to "access 1 year"?