How safe it is to install modded apps on GrapheneOS?

Let's say that I'm on the latest Pixel device with the latest GrapheneOS release.

I have configured GrapheneOS settings for the best security.

I obtain modded APKs from reputable sources.

I scan APKs with VirusTotal (I know that badness enumeration doesn't work, but it doesn't hurt too).

I try to limit permissions as much as possible.

What are the chances of these modded apps doing some real harm?

[deleted] Which reputable sources for modded apk do you have in mind please?

Define "safe" and "real harm."