So you want to add your own custom link types? If the standard 'Hyperlink' and 'Label' categories aren't enough for your workflow then you can create your own.
Firstly you will need to Add a Link to the model which will fall under that category by Right Clicking the object it will be attached to > Links > Add Link.

Then create your link, but where it has a drop down of Hyperlink or Label, just click in this box and type your new category.

This will now be available for all future links on that model.

You can also change whether your new link type is shown as an icon or a text in Options > Interface > Links > User Defined Categories

There are two views, Grid view and

And List View

They both allow you to change the type of Icon to a text label, and the visibility.
The padlock means no changes can be made to add more categories on this screen, they must be made in the model view.
When used to its full potential, your model can be the springboard for other users to access building regulations, schematics, various reports and images of the site in progress, they simply need to go back to the options to change the visibility of the links they need.
Let us know if this is something you are using and if you have any tips you would like to share using the links on the left.