When you want to change SYMBOL statement options, bear in mind two important properties:  SYMBOL statements are both global and additive. This means that

• once defined, they remain in effect until you change them, cancel them, or end the SAS session

• within one SYMBOL statement, you can change the value of one option value without affecting the values of other options.

Let's look at an example. Suppose you submit this statement to set attributes for SYMBOL1.

     symbol1 value=square color=blue
             interpol=needle; 

Later in the same session, submitting the statement below will modify only the plotting symbol. The color and interpolation method will be unchanged.

     symbol1 v=triangle;         

The result of the two statements above is that SYMBOL1 will have blue triangular plotting symbols and needle interpolation.