Yes. If you for example want to place a 930×180 creative on a 728×90 content unit you can easily do so. All you have to do is go to the Campaign overview and then click on Campaign info.
Here you will have to tick of the Any dimension-box which is found under More options.
Giving the campaign the Any dimensions feature will allow the creative to be posted on any content unit regardless of its size. This feature can therefore be very useful if you wish to change the structure of your website for one campaign only.
But because the structure of your website is so easily changed you must be very cautious with this function as it can easily disrupt an entire website depending how the website’s html is coded.