Is there a way to create an unpaid "trial" membergroup?

[truckworks]

Hopefully there is a way to do this without a mod and I'm just too dumb to figure it out. 
 
- Guest decides to register, goes through process 
- Upon registration, member is automatically assigned to "Trial Member" membergroup 
- Trial period lasts 3 weeks, then member is reverted back to guest status without ability to just keep renewing trial 

I attempted to do this via paid subscription (set cost to $0.00, but PayPal kicked it back) and didn't see any potential solutions in the permissions area. 

[Oldiesmann]

There is no way to do that in a default installation. You would need to write a mod to do that.

[truckworks]

What if I am totally incompetent when it comes to coding and/or modification 

[Kindred]

That's why we have the package manager which automatically applies mods for you.

[Colin]

Mod requests or help wanted board would be a good place to start.