Yes, within reason.
You need to have purchased the game within 14 days, and have played it for no more than 2 hours.
Failing that, you do get an additional discount on bundles where you already own some of the games.
Refunding Games with Steam
Steam have a refund policy for games. They go as far as confirming that this policy allows you to repurchase games that go on special.
How to Request a Refund
Valve will, upon request via help.steampowered.com, issue a refund for any title that is requested within 14 days of purchase and has been played for less than 2 hours. Even if you fall outside of the refund rules we've described, you can submit a request and we'll take a look at it.
Additional information and troubleshooting instructions for existing refund requests can be found in our Common Refund Questions FAQ.
- "How To Request A Refund" @ Steam Support
What can I request a refund for?
Valve will, upon request via help.steampowered.com, issue a refund for any title that is requested within 14 days of purchase and has been played for less than 2 hours - this includes online, offline and shared library playtime. Even if you fall outside of the refund rules we've described, you can submit a request and we'll take a look at it.
I bought a game right before it went on sale. Can I get a refund and repurchase it at the sale price?
If you have not already requested a refund, make sure the purchase is eligible and submit a request here.
Please note that approved refunds may take up to 7 days to process.
- "Common Refund Questions" @ Steam Support
Always Double Check the Bundles
When you look at a games store page, you can see the bundles that game is a part of. It is always worth checking the additional bundles. You might find it a better option to directly buy the bundle. You might even consider holding off and purchasing the bundle at a later date, depending on the situation.
Bundles Still Give You Discounts
As Mixxiphoid mentioned, you still get discounts on a bundle, even when you own some of the games. Steam applies a further discount to account for the games you already own. To give a real world example, I own the "Orange Box" collection and "Left 4 Dead 2". These games are a part of the "Valve Complete Pack BUNDLE". At the time of writing this answer, the bundle is selling for
A$213.00 A$19.08; but when they take into account the games I already own, the price goes down to A$146.50 A$13.12.
Bundles are a special discount on a set of products. If you already own some of the products contained in the bundle, purchasing the bundle will allow you to "complete the set", paying only for the products you don't already own while still receiving the full bundle discount on each of those products.
- BUNDLE rollover notification found via the Steam application