If it's just the interrupts you are interested in, then you're fine. Unless I am mistaken, they are not at all dependent on your current paragon and renegade score. The only one I remember being dependent on anything is that your words to Veetor will determine if you get the paragon or renegade interrupt option there. Then there early conversations with Mordin allow you to Renegade interrupt early and then give a Paragon interrupt if you don't take it. Other than that, they are entirely separate and situational.
Conversation options are another story... see below
Yes, the neat thing about the Paragon/Renegade morality in Mass Effect is that it tracks BOTH.
Compare to KOTOR, where you could be lightside OR neutral OR darkside.
So basically, you can play Paragon for your crew and Renegade for everyone else.
My Shepard is Paragon, through and through, but I will occasionally take the Renegade interrupts, usually when dealing with a scumbag.
While this is true, ME2 has a weird way of calculating if the conversation options are available. I don't know what ME1 and 3 do. ME2 compares your total of Renegade or Paragon to the total points that could have been earned so far, which means that each time you don't earn points hurts your ability to make dialogue options in that category for the rest of the game. This seems weird and even unfair, but it makes sense if you see it as building Shepard's personality into someone who wouldn't say certain things. Because it's based on how many points you could have had, that means that it's more about closing off doors because you acted a certain way rather than the doors starting closed and only opening once you've earned enough points. Basically, it allows you to put Shepard as a Paragon or Renegade right from the start if you wish.