smarty : assign var and scope root - scope

Question

I have a template in smarty like this :
Template folder
home.tpl
article.tpl
category.tpl
var.tpl
In each template file (except var.tpl), i include the file var.tpl.
home.tpl have a structure in 1 column
article.tpl have a structure in 2 columns
My template files are like this (home example) :
{include file="$tpl_dir./var.tpl"}
<div class="span{$center_column}" id="center_column">
</div>
In order to change quickly the apparence of my website, i wrote the following lines in var.tpl :
{assign var=center_column_g value=['home'=>'12','article'=>'10'] scope="root"}
{assign var=center_column_default value='10' scope="root"}
{if $center_column_g[$page_name]}
{assign var=center_column value=$center_column_g[$page_name] scope="root"}
{else}
{assign var=center_column value=$center_column_default scope="root"}
{/if}
ps : $page_name is a global variable with the name of each template page.
So with var.tpl, if i can easy change the class of my div #center_column
I have a doubt with this code :
{if $center_column_g[$page_name]}
{assign var=center_column value=$center_column_g[$page_name] scope="root"}
{else}
{assign var=center_column value=$center_column_default scope="root"}
{/if}
Is it right to assign var center_column in the root scope ?