Prevent a WI -> WI link based on WIs type/attributes ?

I have added some new Link Types to RTC and I have a need to prevent
the user from linking some WIs to other WIs based on:

- The source/target WIs type
- The value of the source/target WIs attributes

In the link def I use:
..
itemReferenceType
..

Is there a way to add more constraints here? if not then I guess I
need to add code that would run when adding links - can I get some
instructions on what class to use etc'?

Thank you, if I understand correctly only when the user press 'save' I
will be able to check if the links are ok. I wanted to check this when
the user does the "add link" - is that possible?

I was thinking then maybe to take a diff approach: add a menu action
(available via right-mouse click on a WI) that will enable to add
links. In such a menu action I know the WI type and can activate the
action only for the allowed types.

Is it possible to add menu actions for WI via a standard extension
point?