If you are 'dotting' the file then as you are not invoking it, as such, just including
it in the current script, so the $1 $2 $3 will be the same as the current shell.
So any vars visible in the 'calling' script will be visible in the dotted script anyway.
If you want to reset $1 $2 $3 you can use set
Friday September 2 10:48:00 BST 2005
billym.primadtpdev>set -- `date`
billym.primadtpdev>echo $3 $2 $1
2 September Friday