AJAX callback "alt_text" insufficiently changes links

The AJAX callback "alt_text" is currently used for the following links:

• Subscribing/Unsubscribing from forums
• Subscribing/Unsubscribing from topics
• Bookmarking topics

The problem is that "alt_text" only changes the link title but neither the link nor the icon are changed.
For example after subscribing the link title will be changed to "Unsubscribe topic". Clicking on it again will first ask you if you want to unsubscribe from this forum (which is obviously incorrect) and by clicking on yes it will show an error message.

A possible fix might be adding two new attributes, data-alt-href andd data-alt-icon.