Views generated block - how to override filter on some pages?
I would create a custom module for this, sounds like it could be done quite easily.


Create an admin interface where the 4 default links can be entered.
Create fields on nodes, where the special links can be entered.
In the block view, try to load the node, if possible check for custom links and use default links if needed.


The above solution is good and flexible if you only want links.

If you instead want node references, with the posibility of getting more data, like an image, taxonomy term etc, nodequeue could come in handy instead, as you with views can setup a more sophisticated display easily. It would however become a bit more tricky to override, but could be done via preprocess functions or hook_views_query_alter.