Easy Fix here. Sounds like your load parameter is a Type parameter, not an Instance Parameter. A Type parameter will be the same for all instances of particular family Type. An Instance parameter will be unique for each instance of a given family Type.
You need to edit the family and modify the Parameter, see attached image. If you're struggling with core concepts like this I'd highly recommend that you get yourself some training or review the documentation included with the program.
Kyle Bernhardt Product Line Manager Building Design Suite Autodesk, Inc.
While what Kyle said will certainly work the other option is to simply create a new type. In this case you don't have to go into family editor at all.
If you select one of the "standard" receptacles and click properties, then click the "Edit / New" button in properties dialog you will get another button that says "duplicate". You can create a new receptacle, called receptacle 1200 VA and set the load to 1200 VA, and then another new type called receptacle 650 VA and set the load to 650 VA.
If you are familiar with AutoCAD you can think of Type parameters similar to the way that you think of the graphics on a standard AutoCAD block, and think of instance parameters similar to the way that you think of attributes on a standard AutoCAD block. Each "insertion" of a block will have the same basic graphics (or type parameters), but each insertion of the block can have different attributes (or instance parameters).