How to change default cell formats in Excel 2011?

My employer has provided me with Office 2011 on my MBP workstation, running Mountain Lion. They use networked Excel docs almost exclusively, so I need to adapt to it. There's a handy toolbar item for working with default cell formats:

I've got three or four formats I use to code item statuses in the project sheets (to do, problem, incomplete, complete), and I can figure out how to modify these default styles to my preference ... and delete the couple dozen I will never use. The problem is, whenever I open a new doc, all my custom styles are reset and the extraneous defaults I deleted have returned.

Is there a way to permanently change these default styles? I want the changes to persist both for new docs I create, and when opening docs someone else has created. Google has proved fruitless for me, but my search-fu is not the strongest.

PS (Though I would prefer to, please no comments about switching to Numbers. Already had that conversation with the boss.)

For existing (or the one you get from others) Excel documents where you have a lots of data in it, try using the down arrow (under the format window).

It will open new window where you can choose a new format there.

Next right click on the cells you want to modify, or just create new cells.

Another way for existing documents you get from others do following:
Open and than click on the "Import Cell styles" than select your format file (both files have to be open at same time).

For new documents use your saved template.

PS. One day you will succeed giving your template to your coworkers and teaching them to use it, so you do not have to reformat theirs.

Here is my screen capture showing the original and SAMPLE after modifying. Hope this helped, and you can impress your boss with your excel skills.