Make parameter disabled depending on layer type.

Is it possible to make a parameter disabled dependant on the type of layer it is applied to?  For example, if I apply the plugin to a TextLayer can I disable certain params, but enable them if I apply the same plugin to an Image layer?

In the SDK, I read, that PF_PUI_DISABLED "Disables (grays out) the parameter, usually in response to PF_Cmd_USER_CHANGED_PARAM" but how would I disable the parameter immediately by checking the type of layer.  I was thinking of using javacript to detect the layer type, but maybe that's too much overhead.  Is there any way to:

1.  Programatically fire off PF_Cmd_USER_CHANGED_PARAM

2.  Detect the layer type with the SDK instead of resorting to calling a javascript from within the plugin's code?

Thank you for your time and help!

Best,
Arie