Users get "real" pricing after registration

Probably pretty simple, but I'm in a bit of a hurry.

I would like all prices "line-through" until user registers and logs in, then "real" prices are displayed. I also want to put a "register for special pricing" button below each line-through price (goes away when user logs in).

Strict requirements from manufacturer to not display pricing below MSRP to the "public".

Is there an easy way to not modify the tpl directly? I want to make upgrades as seamless as possible, without finding diffs and customizing each time. Sorry, I'm a php novice.

That's what in my thought