Yes, it is possible to change the format used for all the calculated/displayed numbers in a cross-tabular table. If you are using PROC TABULATE or the Summary Tables Task, this is very easy to do. To change ALL numeric formats in the table, if you right-click in the table, when you are in "design" mode on the Summary Tables dialog box, there will be a choice for "Table Properties" and under Table Properties pop up window, there will be a tab for "Formats" -- on this tab, you can choose the format and number of decimal places. You can also select a standard numeric format to use or a user-defined format. There are up and down arrows that allow you to select the format overall width and number of decimal places.
For example, if I pick an overall width of 12 and 3 decimal places, then this is what EG generates for the PROC TABULATE statement:
PROC TABULATE DATA=XXXX.YYYY FORMAT=12.3 ;
If there is a particular row or column statistic that you want to give a separate format, then you might need to right click on a cell header and modify the "Data Properties" format to be a different format (such as a different format for a grand total or ALL column).