Now, I haven't used a ton of IP's at Safeway at once especially all for the same item (I have been using these IP's mixed with regular coupons, my mom used 6 printables at once successfully). You can show them the unique codes to prove that they're legit but it might be easier to split them into smaller groups (in twos!). You could also run into cashiers who might say no, because according Safeway's policy they don't have to take IP's worth more than 50% of the item's price and $1 is just a smidge over half of $1.99- I don't think that's likely, but you never really know. Whatever you do, remember that you get one $2 catalina for every 2 butters you buy! These butters are also free at Albertsons and Fred Meyers as well, and you can use the catalinas earned to buy more butters (provided you have a filler item each time). For more info on how these are free, read my original post about it.
I hope that explained everything well, but if you have questions- please leave me a comment and I'll respond as quickly as I can!