Hello there im looking for a formula that will fill all blank cell from A1 to
AA1020 with "0" without affecting the blank cell properties i.e. filled
colors, sizes, etc. thanks

You may already have understood this, palups, but no formula will fill OTHER
cells for you; it'll only affect the cell it's typed in. That's by design;
otherwise we'd all be capable of royally messing ourselves up.

If you have a large area that has a lot of formatting in it but no data,
then what you want is a way to copy 0 into the DATA of each cell without
affecting the FORMATTING that's already there. That's easy: Put a 0 in one
cell, then copy it, highlight the area you want to paste to (A1 to AA1020),
then hit not Paste but Paste Special from the same Edit menu. The Paste
Special window pops up; select Values and hit OK, and it'll copy JUST THE
VALUE into each cell, but not the formatting. Explore that Paste-Special
window; it has other useful capabilities too.

If you already have data in this large area, and don't want to start over,
the best you can do is create a quick macro to look at each cell in the area
and, if it doesn't already have data in it, put 0 into it. If you don't
already know how to do that, check in the Excel Programming forum.