Should You Tell Colleges About Post-Application Accomplishments?
I was just elected president of my school's engineering club and I won first place in a marketing competition. Should I email my colleges and tell them about this while they're reviewing my applications?
The short version is this: Sure go ahead. Since you've got a two-for-the-price-of-one situation here, it's fine to write a brief email to your colleges to update them on both of your new achievements.
BUT ... the longer version is this: Depending on where you're applying and what other accomplishments are on your application already, these new ones may not move the needle. If you're applying to the most competitive colleges, then landing the presidency of your school engineering club will be viewed as worthwhile but won't affect your admission verdicts. At somewhat less selective colleges, however, it will carry a bit more clout, especially if you're aiming for a STEM major. Similarly, only a big-deal marketing competition win is worth reporting to the hyper-selective schools.
Since "The Dean" can't view these recent accolades in the context of where you hope to be accepted and what you've already reported (e.g., other leadership roles and awards), you should determine for yourself if this good news is also going to be regarded by your colleges as big news and then decide to notify colleges ... or not ... accordingly.
Finally, are you expecting any college verdicts before your first semester ends? If not, then hold off until the semester is over and then you can send all of your colleges a short update letter that covers your major accomplishments since you first applied in the fall. You'll find a sample update letter here.