You can't easily create new tag, but you can modify the [AMOUNT] tag to not show the currency. In this file:
/administrator/components/com_dtregister/lib/tagparser.php
Find this:
function amount($recipient){
global $currency_code;
$user = $this->getuser($recipient);
return DTreg::displayRate($user->TableFee->formatamount($user->TableFee->fee),$currency_code);
}
Change it to this:
function amount($recipient){
global $currency_code;
$user = $this->getuser($recipient);
return $user->TableFee->formatamount($user->TableFee->fee);
}
That should do the trick. You could make a similar change to other tags like [AMOUNT_DUE] if you want or need to.