For restricting the number of decimals of an attribute of type DOUBLE for all instances, use the statement LAYOUT in the AttributeNumericDomain facet of the respective attribute.
Example:
If you want to display the full number of decimals in the Notebook, but only two decimals in the graphical representation, the solution would be using the function round() as described in the code snippet below (for displaying two decimals):

The function round(x) returns the closest integer.