No. The coverage in force at the moment of the crash is what governs your claim — UM/UIM cannot be added retroactively. That is why the time to review your policy is now, before anything happens.

When you review it, look at the limits too: minimum-limit UM coverage may not come close to covering a serious injury. Underinsured motorist (UIM) coverage also matters — it fills the gap when the at-fault driver has insurance, but not enough.