I use openSUSE (the Tumbleweed rolling release specifically) for
everything, and from my experience the live USBs are persistent by
default.
If you want to use the same live installation for a long period of time,
I would recommend just installing directly to the USB stick instead of
using the live ISO. With Tumbleweed you can do this by burning the
net-install ISO (not the DVD ISO) to a USB stick and then once you have
booted it, simply tell it to install to the USB drive as opposed to your
main disk and install as usual.
--
"If you can't explain it simply, you don't understand it well enough."
- Attributed to Albert Einstein