ok, replace...
Code:
<select id="product_avail" name="amount"{if $active_modules.Product_Options ne '' && $product_options ne ''} onchange="check_wholesale(this.value);"{/if}>
{section name=quantity loop=$mq start=$start_quantity}
<option value="{%quantity.index%}"{if $smarty.get.quantity eq %quantity.index%} selected="selected"{/if}>{%quantity.index%}</option>
{/section}
</select>
With...
Code:
{if $current_category.categoryid eq "123"}
<select id="product_avail" name="amount"{if $active_modules.Product_Options ne '' && $product_options ne ''} onchange="check_wholesale(this.value);"{/if}>
{section name=quantity loop=$mq start=$start_quantity start=2 step=2}
<option value="{%quantity.index%}"{if $smarty.get.quantity eq %quantity.index%} selected="selected"{/if}>{%quantity.index%}</option>
{/section}
</select>
{else}
<select id="product_avail" name="amount"{if $active_modules.Product_Options ne '' && $product_options ne ''} onchange="check_wholesale(this.value);"{/if}>
{section name=quantity loop=$mq start=$start_quantity}
<option value="{%quantity.index%}"{if $smarty.get.quantity eq %quantity.index%} selected="selected"{/if}>{%quantity.index%}</option>
{/section}
</select>
{/if}