Yes, everyone says that a lot about upgrading and mods etc. Here's the secret: if you have highly modified code, change the mods to their own unique .tpl files and modify those. It's even easier to have one template with Smarty includes for all of your customizations. Then, when you upgrade NOTHING will ever be affected and you just have to add the includes (your mods wouldn't change).
But, regarding flash in the product.tpl ... I have one hack that works but isn't pretty, here's a quickie from a product.tpl. You'll have to change anything that is unique to my code, like categories numbers. I have used deonya's detailed image mod and then this in the product.tpl. Be sure if you use deonya's mod (from the forum) to make the correction as specified through the thread.
If this doesn't make sense to you, then you may want to consider getting Boomer's (cart-labs) SFW mod. But, what I am doing here is: if there is no #1 detailed image (with doenya's mod) and if the category isn't X, Y or Z then use the SWF that is named after the product code.
Code:
{if $images.0.avail eq "Y"}
{if $images.0.tmbn_url}
[img]{$images.0.tmbn_url}[/img]
{else}
[img]{$xcart_web_dir}/product_image.php?imageid={$images.0.imageid}[/img]
{/if}
{elseif $cat eq XXX} [b](XXX equals a category where I have NO image)[/b]
{**************************
{include file="product_thumbnail.tpl" productid=$product.productid
image_x=$config.Appearance.thumbnail_width product=$product.product
tmbn_url=$product.tmbn_url id="product_thumbnail"}
**************************}
{else}
<span>
<table cellspacing="0" cellpadding="0" border="0" bgcolor="#C8CDD0">
<tr><td align=center valign=top>
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0" WIDTH="247" HEIGHT="227" id="flashViewer">
<param name="movie" value="http://positive_URL_to your SFF_files/Your_SWF/{$product.productcode}.swf" bgcolor=FFFFFF>
<embed src="http://positive_URL_to your SFF_files/Your_SWF/{$product.productcode}.swf" bgcolor=#FFFFFF WIDTH="247" HEIGHT="227" NAME="flashViewer" TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/go/getflashplayer">
</embed>
</object>
</td></tr>
</table>
</span>
{/if}