I've got a page that already has got the $_GET array initialized, so when a webpage redirects there (by having an oAuth token) it appends the ?token=36264747 towards the finish.

It is possible to method to write an .htaccess apply for an Apache server that will either strip that question mark or (better) change it by having an ampersand?

You'll need the qsappend or QSA (query string append) flag for RewriteRule:

RewriteRule ^foo(.*)bar$ index.php?token=$1 [QSA]

will append token=$1 towards the query string (the $_GET part), using ? or & as appropriate.