If you need to get an action to use a shared repository and NOT it's own rep. there is a way:
Create a new Test in QTP. Then goto Test -> Settings -> Resources Tab and set this new Test to use a Shared Rep. point it to the one you want.
Now save this test and open your original one. Copy the code out from the Expert View and then paste it back into the new test you created. Save up the new one and presto, you have the previous test now using your shared rep.