The tutorial is simple and as you just add the code to a gadget you can easily remove it after Christmas.
Add Christmas Banner To Your Blog
Step 1. In your Blogger dashboard click > Design > Add A Gadget > Choose 'Html/Javascript' :
Step 2. Copy and paste the following code into the Html/Javascript gadget :
<a href='http://www.createtheblogger.blogspot.com'><img alt='Best Blogger Tips' src='https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAH6CBD-AUjFNI-vLZwNgx-R5oKymOEbxMpRKUDY_tGPIrjCQB_Y-NuBAIq44oWLLOhs0GqbQlrMI1QBj64vvS8fxl5Uj85_hYSYszmiDx3fKku6yvgZNrOTluqeT5VAq6YH7BjhwbZ6sV/s1600/best+blogger+tips.png'/></a><div style='position: fixed; top: 0%; right: 0%;'/>
<a href="http://www.spiceupyourblog.com" target="_blank"><img alt="Blog Tips" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDZ-qyJJfO-oeAoObfav1CvTVgpbsXVIfaFCR9CZ5pY1b0sNWPH7yZN5YTYJXM6wJDg6l9mQrLdkqVYYo3UeQXiHf7fNwCSw9IxXVUfiqfucoTqgcb15-CbSI5a29iz7Rar2WTxh09uW2r/s1600/merry+christmas+blogger+banner.gif"/></a>
</div>
Step 3. Save the gadget and you gadget is in place, Easy.
Check out our Blogger Gadgets.