Tsk. If I were the SG there's no way I'd ever allow Diedne-descended magi in House Tremere, not even as NPCs. But seeing as it's happened...
First of all, good points have been made about a Dark Secret not being an automatic PC death sentence. But in this case I think the chances of getting killed should be very high. Having said that...
House Tremere is going to look fairly feeble and ridiculous if it emerges that it has a Diedne lineage hiding in its ranks. Certain senior Tremere magi with very pragmatic attitudes (pick them very carefully) might just be open to the idea of keeping the whole thing very quiet if you share the secrets of your Diedne heritage exclusively with them.
On the other hand, it's not just House Tremere who'll have it in for you. Most of House Flambeau will be out for your blood as well, and so will plenty of other Christian magi who see the eradication of a gang of bloodthirsty pagans as A Good Thing. Nevertheless, if you haven't broken any laws there isn't much a Tribunal can do to you. Just watch out for hundreds of magi wanting to declare Wizard Wars against you.
Well, you can certainly research an ability you have since that's the necessary step to change a mystery virtue/twilight gained virtue into a teachable virtue. That'll generate huge quantities of lab-texts, and make you a hero of the Order and gain a crapload of prestige for the Tremere. The "early notes", in which you adapt your ::cough:: Twilight-gained insight ::cough:: into something to research were clearly lost in the labfire when you tried to use a failed research direction and sponted a huge fire-ball. Fortunately, the bulk were saved.
And, of course, once you've accrued enough lab-texts to show that your research is going places, you can make requests of Durenmar and the Tremere stores for Diedne artifacts for study to help, thus being true to your house and your lineage.
Since this is about spontanious magic, you have numerous breaktroughs that were not breakthroughs, but just luck. And, you will have to research all sorts of magic, including creo ignem and perdo animal