You should modify /skin1/main/product_details.tpl
Find in this template (line about 281):
Code:
<option value='Y'{if $product.free_tax eq 'Y'} selected="selected"{/if}>{$lng.lbl_yes}</option>
and change it to
Code:
<option value='Y'{if $product.free_tax eq 'Y' || $product.productid eq ""} selected="selected"{/if}>{$lng.lbl_yes}</option>
This allow to assign free tax if new product being added.
Also with shipping, find line ( about 308 ):
Code:
<option value='Y'{if $product.free_shipping eq 'Y'} selected="selected"{/if}>{$lng.lbl_yes}</option>
and change it to
Code:
<option value='Y'{if $product.free_shipping eq 'Y' || $product.productid eq ""} selected="selected"{/if}>{$lng.lbl_yes}</option>
This allow to assign free shipping by default.