Is it possible to have a custom action List Item Menu in a document library on a specific content type, created in SPD 2010? In code I know is possible, but I'd rather try it out in SP Designer. Also, is it possible to enable specific security rights during its creation?
It's definitely possible.
Open the document library in SPD. You will have "Custom Action" button on the ribbon, where you can select "List Item Menu" custom action:
Then, on the form which appears, use vertical scrollbar (many people don't notice it's there) to scroll the contents of the form down. You will see "Rights" box there:
Unfortunately it's just a plain text field, you will get no hints of what should be there. Fortunately I can tell you that :) You must use values of the SPBasePermissions enumeration there. AFAICR, you can define several values, separating them by ",".
Btw, another trick here is that you can use
Well, as you can see, the interface is not very obvious, but nevertheless it exists :)
In addition to Andrey's answer...
Put this in your "Navigate to Url" field in the custom action.
and put this function in your master page or a form html webpart on your page
then whatever you want to run on a specific content type put in here
Tested in SP2010 Foundation.
Here are the two solutions, powershell and also VS2010 feature, both tested: http://zoraradosavlevici.wordpress.com/2013/03/01/add-list-item-menu-custom-action-to-a-specific-content-type-sp-2010/