I want to display a points feature giving each point a color depending on the range of values within which it falls, because I have more than 120.000 values (one for each point) and don't want one color for each point. I know I can group values in symbology by selecting and right clicking on them, but it gets a very slow process when I have so many values, the process seems even to get stuck. Is there a way to get this grouping by assigning rules? For example I would have four ranges of values (=0, 0< value <=1, 1< value <=10, value >10). I know I could also create a new field and assign range values to each row after attribute selections, but I would avoid that.
If I understand your problem correctly, you should be able to solve it using Symbology => Quantities => Graduated Colors.
Choose the desired Field and specify the number of classes and then "Classify". Using the manual classification method you should be able to define break values.
If you are planning to use a representation, then you will have a "RuleID" field for that representation anyway. The RuleID can be edited just like any other field.
So, set up your representation and then use Select By Attributes to select the ranges you want and use Calculate Field on RuleID to set the rule to use.
I am not understanding, though, why a Quantities > Graduated Colors symbology definition would not achieve the same thing. Use Manual Breaks and then you can individually edit each symbol to use colors other than the graduated colors.