[Feature request] On the expiration of notifications.

[Linuxghost]

Thank you for your work on batsignal. I've been using it for about 6 weeks and love the simplicity of it.
Now the -e option "cause notifications to expire".
I had that on at the first couple of weeks only to find out that often I missed a notification to plug in the charger.
So now I turned the -e option off.
Now when you have the "Battery charging (-P) or Battery uncharging (-U) option" you get notifications that better expire because you don't need to do something.
My question is would it be possible to use the -e option on a per-level base?
e.g. -Pe and -Ue?
For clarity; here's my batsignal conf.