There is a bug in AutoCAD P&ID where a Control Valve cannot be substituted with another valve type. You will only be shown with a list of Instruments to be substituted. Read related post in the forums here. This seems to be fixed in 2014 Extension 1 according to Craig in the forum but existing control valves will not be fixed. If you don' want to install Extension 1 or you want existing control valves to be fixed, try it out.
Currently, this is only available for 2014 version. I'll update in a few days for the other version if someone confirmed this works. So first, go to the download page and download LazPlantBrowser if you have not already done so. Then download Lazcad.PlantBrowser.ControlValveFix from the plugins section. Unzip the dll and place it inside the 2014\Addins folder. Now run AutoCAD P&ID, open LazPlantBrowser, and you should be able to see "Fix Control Valve" in the command selection list. (Please close all P&ID drawing before running this command).
How It Works?
Each Style has a corresponding block. This issue is caused because wrong style is assigned to the Control Valve (caused by a bug when a drawing is saved). The plugin works by finding the corresponding style based on the block name (so this does not work with converted block), then it will reassign the original style to that block.
* As always, backup first because I'll not be responsible for any damage caused to your drawings..