Completely hypothetical, but let’s say I apply EA or ED and am deferred. If something happens in-between then and the regular decision date, could I update the college that deferred me with the new thing? Are there strict rules about this?
I would just email or call them with your applicant number and let them know about the update.
It is common practice to email an admission officer if there is a significant update to an application. It is appropriate to relay a significant achievement that happened between when the application is filed and when a decision is made (doesn’t just have to be for an EA/ED deferral). Just keep it short and to the point as admission officers are busy.