Generally the disabled buttons are a high-level layout feature, rather than a hard, low-level lock on data writing. You can edit virtually anything in linked data using the bpy API as well - these changes will just be ignored on writing .blend files. The disabled buttons are merely a helper to prevent confusion and lost time when editing such volatile linked data.

That being said, it would be nice to extend the disabled layout to the UI templates used for curve and color ramp widgets. Problem is that these are using old-school direct button drawing, which circumvents the "disabled" flag of the layout. Will check with other devs if disabling buttons and ui handlers based on layouts there is feasible.

For reference:

implementation of the curve widget ui drawing