systpl Alternative?

Hey,

I know you can change the current template of WHMCS client area via url, using /?systpl=portal, but can you do it via the .tpl files?

For example:

{if $currency.code eq "USD"}
systpl="us"
{else}
systpl="default"
{/if}

Thanks in advance, I hope this is possible as it's not that effective doing it by URL for me, due to the current template dependant on currency.

Kind Regards,

John.