If a person accidently overdosed on humalog, would an epipen (epinephrine) help?

Not directly: The result of an overdose of Humalog (insulin lispro) would be a low blood sugar; although Epinephrine would raise the blood sugar somewhat, the appropriate treatment would glucose (sugar) to avoid a dangerous fall in blood sugar while the effect of Insulin wears off.

Glucagon is better: Glucagon will raise the blood sugar faster and with less side effects. It has to be injected like epinephrine.