As Epic found out, not if you want to remain on Google's good side. They were facing sanctions from Google due to their sideloading of Fortnight onto Android phones and tablets.

What “sanctions” were they facing? They were called out because their app was a security nightmare.

https://www.cnet.com/news/fortnites-battle-royale-with-andro...

My understanding is that the "vulnerability" here also exists on every computer or other device on which you download an installer to a public folder--any application can watch that folder and silently replace the file with another when the download completes. There's nothing special about that. Android has a secure internal storage area--but internal storage is often limited. It's gotten better, but my previous phone only had 8gb for both the OS and data to share.