should htaccess be writable?

should .htaccess be writable? the reason i ask is because i’m using permalinks and everything is working fine except for XDforum, which needs me to add these lines:

RewriteRule !xdforum/ /index.php [L]
RewriteRule ^xdforum/([^/\(\)]*)/?([^/\(\)]*)/?([^/\(\)]*)/?([^/\(\)]*)/?([^/\(\)]*)/?([^/\(\)]*)/?([^/\(\)]*)/?(\([^/\(\)]*\))?/? /index.php?pagename=xdforum&xdforum_action=$1&xf_id=$3&xt_id=$5&xp_id=$6&start=$8&pstart=$8 [QSA,L]

when i add these, everything works fine, including xdforum. however, the .htaccess keeps getting rewritten somehow, reverting back to the original file, which looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

so my question is, if i add the xdforum lines and then make .htaccess, will it stay that way? and if so, is it a bad thing to have .htaccess not writable?